Nodular cast iron

Abstract

Provided are a nodular cast iron and a preparation method therefor, a sand mold casting method for a nodular cast iron part, an iron mold casting method for a nodular cast iron part, a forming method for a nodular cast iron part, a nodular cast iron part and a wind generating set. In the nodular cast iron, based on the total mass of the nodular cast iron, the nodular cast iron comprises, in percentages by mass: 3.6-3.8 wt% of C, 2.3-2.6 wt% of Si, Mn≤0.14 wt%, and 0.20-0.55 wt% of Ni. The nodular cast iron has a tensile strength of larger than 400 MPa, a yield strength of larger than 280 MPa, and a low-temperature impact energy at -20°C of larger than 7 J, and can be widely applied to wind generating sets.

Description

Ductile iron Technical Field

[0001] The present invention relates to the fields of metal materials and casting technology, and in particular to ductile iron and a preparation method thereof, a sand casting method for ductile iron parts, an iron mold casting method for ductile iron parts, a molding method for ductile iron parts, ductile iron parts, and a wind turbine generator set. Background Art

[0002] With the continuous development of ductile iron technology, ductile iron has gradually replaced cast steel and become a new type of metal material. As a type of ductile iron, cast ferritic ductile iron has been widely used in engineering machinery, basic components of injection molding machines, basic components of die-casting machines, and wind power generation foundations or key components.

[0003] Current research on ductile iron for wind power applications focuses on how to maintain existing strength while ensuring impact energy meets performance requirements at low temperatures and preventing casting fracture. However, existing chemical formulations and production processes cannot guarantee a significant increase in strength while also meeting low-temperature impact energy requirements. Existing research indicates that increasing strength while maintaining low-temperature impact energy is a conflicting proposition: increasing strength inevitably compromises low-temperature impact energy. Addressing this challenge is a key area of ​​research.

[0004] Furthermore, the main shaft of a wind turbine connects the impeller and gearbox, bearing complex axial and radial loads. As wind turbine power increases, it becomes increasingly necessary to improve the performance of the main shaft. This performance is primarily determined by the material and the molding process used. Existing main shafts are unable to meet these higher performance requirements. Summary of the Invention

[0005] The present invention is proposed to overcome the shortcomings of the above-mentioned prior art. The present invention provides a ductile iron and a preparation method thereof, wherein the ductile iron has a tensile strength greater than 400 MPa, a yield strength greater than 280 MPa, and a low-temperature impact energy greater than 7 J at -20°C.

[0006] According to an embodiment of the present invention, there is provided a ductile iron, which may include, based on the total mass of the ductile iron, the following components in mass percentage: C 3.6-3.8wt%, Si 2.3-2.6wt%, Mn≤0.14wt%, and Ni 0.20-0.55wt%.

[0007] In an embodiment, the ductile iron may further include, by mass percentage: V 0.001-0.01 wt %, Ti 0.02-0.03 wt %.

[0008] In the embodiment, the ductile iron may further include, by mass percentage: P≤0.035wt%, S≤0.02wt%, Cr≤0.025wt%, Mg 残 0.035-0.060wt%.

[0009] In an embodiment, the matrix of the ductile iron may be ferrite.

[0010] In an embodiment, the content of Si may be in the range of 2.30-2.49 wt %.

[0011] In an embodiment, the content of Si may be in the range of 2.35-2.49 wt %.

[0012] In an embodiment, the content of Si may be in the range of 2.39-2.45 wt %.

[0013] In an embodiment, the content of Si may be in the range of 2.30-2.40 wt %.

[0014] In an embodiment, the content of Mn may be in the range of 0.10-0.12 wt %.

[0015] In an embodiment, the content of S may be less than 0.015 wt %.

[0016] In an embodiment, the content of Ni may be in the range of 0.35-0.55 wt %.

[0017] In an embodiment, the content of Ni may be in the range of 0.35-0.45 wt %.

[0018] In the embodiment, Mg 残 The content of may be in the range of 0.040-0.054 wt%.

[0019] The ductile iron according to the embodiment of the present invention may have a tensile strength greater than 400 MPa, a yield strength greater than 280 MPa, and a low-temperature impact energy greater than 7J at -20°C.

[0020] According to an embodiment of the present invention, a casting is provided. The casting may include ductile iron.

[0021] In an embodiment, the wall thickness of the casting may be greater than or equal to 60 mm.

[0022] According to an embodiment of the present invention, a wind turbine generator set is provided. The wind turbine generator set may include a casting.

[0023] According to an embodiment of the present invention, a method for preparing ductile iron is provided, and the method may include the following steps:

[0024] (1) Smelting: Carburizing materials including pig iron and smelting them into molten iron;

[0025] (2) Spheroidizing and inoculating: spheroidizing and inoculating the molten iron obtained from step (1); and

[0026] (3) Pouring: pouring the molten iron obtained from step (2),

[0027] Wherein, in step (1) and / or step (2), the preparation method further comprises microalloying, the microalloying comprising adding Ni, adding a spheroidizing agent containing Si and an inoculant containing Si in step (2), and adding a flow inoculant containing Si in step (3), wherein, based on the total mass of the molten iron, the content of Ni is 0.20-0.55wt%, the content of Si is 2.3-2.6wt%, and the content of Mn is less than or equal to 0.14wt%.

[0028] In an embodiment, based on the total mass of the molten iron, in step (1), the content of Si included in the material is in the range of 1.4-1.6 wt %. In step (2), a spheroidizing agent containing Si and an inoculant containing Si are added so that the content of Si is in the range of 2.25-2.45 wt %, and in step (3), a flow-in-stream inoculant containing Si is added so that the content of Si is in the range of 2.3-2.6 wt %.

[0029] In an embodiment, the spheroidizer includes 40-50 wt% of Si by mass based on the total mass of the spheroidizer, the inoculant includes 75±3 wt% of Si by mass based on the total mass of the inoculant, and the inoculant includes 70-80 wt% of Si by mass based on the total mass of the inoculant.

[0030] In an embodiment, based on the total mass of the inoculant, the inoculant comprises, by mass percentage, the following: Si 75±3wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al <1.5wt%, with the remainder being iron. Based on the total mass of the spheroidizer, the inoculant comprises, by mass percentage, the following: Mg 4.5-6wt%, RE 0.15-0.3wt%, Si 40-50wt%, with the remainder being iron. Based on the total mass of the inoculant, the inoculant comprises, by mass percentage, the following: Si 70-80wt%, Bi 0.5-2.5wt%, Ca ≤2.0wt%, Al ≤2.0wt%, with the remainder being Fe.

[0031] In an embodiment, in step (2), the amount of inoculant added is 0.35-0.67wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.0-1.3wt% of the total mass of the molten iron, and in step (3), the amount of inoculant added is 0.08-0.2wt% of the total mass of the molten iron.

[0032] In an embodiment, the inoculant in step (2) includes a primary inoculant and a covering inoculant, wherein the primary inoculant includes 75±3 wt % of Si by mass based on the total mass of the primary inoculant, and wherein the covering inoculant includes 75±3 wt % of Si by mass based on the total mass of the covering inoculant.

[0033] In an embodiment, based on the total mass of the primary inoculant, the primary inoculant comprises, by mass percentage, the following: Si 75±3wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al <1.5wt%, with the remainder being iron. Based on the total mass of the covering inoculant, the covering inoculant comprises, by mass percentage, the following: Si 75±3wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al <1.5wt%, with the remainder being iron.

[0034] In an embodiment, in step (2), the amount of the primary inoculant added is 0.30-0.55 wt% of the total mass of the molten iron, and the amount of the covering inoculant added is 0.05-0.12 wt% of the total mass of the molten iron.

[0035] In an embodiment, Mg is added in step (2) such that the content of Mg is in the range of 0.045-0.078 wt % based on the total mass of the molten iron.

[0036] In an embodiment, the spheroidizing agent includes 4.5-6.5 wt% of Mg by mass percentage based on the total mass of the spheroidizing agent, and the amount of the spheroidizing agent added in step (2) is 1.0-1.3 wt% of the total mass of the molten iron.

[0037] In an embodiment, in step (1) and / or step (2), the amount of Ni added is 0.2-0.4 wt% of the total mass of the molten iron.

[0038] In an embodiment, the microalloying in step (1) and / or step (2) includes adding Ni such that the content of Ni is in the range of 0.20-0.55 wt % of the total mass of the molten iron.

[0039] In an embodiment, in step (1) and / or step (2), the microalloying treatment further comprises adding TiC to the molten iron, wherein the amount of TiC added is 0.01-0.03 wt % of the total mass of the molten iron.

[0040] In the embodiment, the pig iron in step (1) is pig iron of grade Q10 or above.

[0041] In the embodiment, the content of Mn is in the range of 0.10-0.12 wt % based on the total mass of the molten iron.

[0042] In an embodiment, the content of Mn is adjusted in step (1) so that the content of Mn in step (1) is in the range of 0.10-0.12 wt% of the total mass of the molten iron.

[0043] In the embodiment, the content of Ni is 0.35-0.45 wt % based on the total mass of the molten iron.

[0044] In the embodiment, the content of V is 0.001-0.01 wt % based on the total mass of the molten iron.

[0045] In the embodiment, the content of Si is 2.39-2.45 wt % based on the total mass of the molten iron.

[0046] In the embodiment, the content of Si is 2.30-2.40 wt % based on the total mass of the molten iron.

[0047] The ductile iron according to the embodiments of the present invention has a well-developed core structure, essentially free of irregular graphite such as fragmented graphite. The ductile iron exhibits a tensile strength exceeding 400 MPa and a yield strength exceeding 280 MPa. Furthermore, its low-temperature impact energy at -20°C exceeds 7 J, significantly improving the mechanical properties of large-section ductile iron. Therefore, the high-toughness, ultra-high-strength ferritic ductile iron provided by the present invention is particularly suitable for mass production of large-section castings and other key components in wind turbines.

[0048] An object of the present invention is to provide a sand casting method for ductile iron castings, which can improve the comprehensive mechanical properties of the ductile iron castings.

[0049] Another object of the present invention is to provide a sand casting method for ductile iron castings that can improve the structural density of ductile iron castings and reduce the number of shrinkage cavities.

[0050] Another object of the present invention is to provide a ductile iron casting and a wind turbine generator set with improved comprehensive mechanical properties.

[0051] According to one aspect of the present invention, a sand casting method for a ductile iron casting is provided. The sand casting method comprises: preparing a mold; preparing a sand mold using the mold to prepare the sand mold, the sand mold including a mold cavity; pouring molten iron into the mold cavity, and forming the ductile iron casting after cooling and solidification. The ductile iron casting comprises, by mass percentage, the following: C 3.6-3.8wt%, Si 2.3-2.6wt%, Mn ≤ 0.14wt%, and Ni 0.20-0.55wt%.

[0052] Optionally, the sand mold includes an outer sand mold and an inner sand core that surround the mold cavity, and the sand mold also includes an external chill and / or an internal chill, the external chill is arranged around the mold cavity in the outer sand mold and exposed from the mold cavity, and the internal chill is arranged around the mold cavity in the inner sand core and exposed from the mold cavity.

[0053] Optionally, a ratio of the thickness of the external chill and / or the internal chill to the thickness of the portion of the ductile iron casting on which the external chill and / or the internal chill is covered is 0.5-1.5.

[0054] Optionally, the ductile iron casting is the main shaft of a wind turbine generator set, and the main shaft includes a shaft body, a large flange arranged at one axial end of the shaft body, a trumpet-shaped connecting piece connecting the shaft body and the large flange, and a small flange arranged at the other axial end of the shaft body.

[0055] Optionally, the external chill includes a first formed chill and a second formed chill, the first formed chill is arranged at a position corresponding to the upper end surface of the large flange and the outer peripheral surface of the trumpet-shaped connecting piece, and the second formed chill is arranged at a position corresponding to the lower end surface of the large flange.

[0056] Optionally, each of the first forming chill and the second forming chill is formed into at least two sections around the cavity.

[0057] Optionally, the thickness of each of the first formed chill and the second formed chill is greater than or equal to 200 mm.

[0058] Optionally, the coverage rate of the first formed chill is greater than or equal to 90%, and / or the coverage rate of the second formed chill is greater than or equal to 80%.

[0059] Optionally, the external chiller is further provided at a position corresponding to the outer peripheral surface of the shaft body and the outer peripheral surface and / or the upper end surface of the small flange.

[0060] Optionally, the internal chiller is arranged at a position corresponding to the inner circumference of the trumpet-shaped connecting piece.

[0061] Optionally, the internal chiller is further provided at a position corresponding to the inner end surface of the small flange.

[0062] Optionally, the pouring system of the molten iron is a bottom pouring system, the pouring temperature of the molten iron is 1330-1360° C., and the pouring speed of the molten iron is 100-150 kg / s.

[0063] Optionally, the sand mold includes a riser, and the riser includes at least one of a top riser, a middle section riser and a heat-generating riser. The top riser is arranged at a position corresponding to the outer end of the small flange, the middle section riser is arranged at a position corresponding to the outer wall of the shaft body, and the heat-generating riser is arranged at a position corresponding to the inner cavity of the trumpet-shaped connector.

[0064] According to another aspect of the present invention, a ductile iron casting is provided, wherein the ductile iron casting is formed by the above-mentioned sand casting method.

[0065] Optionally, the wall thickness of the ductile iron casting is greater than or equal to 60 mm.

[0066] Optionally, the ductile iron casting is the main shaft of a wind turbine generator set, and the main shaft includes a shaft body, a large flange arranged at one axial end of the shaft body, a trumpet-shaped connecting piece connecting the shaft body and the large flange, and a small flange arranged at the other axial end of the shaft body, and the outer diameter of the shaft body is greater than or equal to 1.0m.

[0067] According to another aspect of the present invention, a wind turbine generator set is provided, comprising the ductile iron casting as described above.

[0068] According to the sand casting method of the ductile iron casting of the present invention, the comprehensive mechanical properties of the ductile iron casting can be improved by controlling the composition of the ductile iron casting and / or the sand casting method.

[0069] According to the sand casting method of the ductile iron casting of the present invention, by controlling the composition of the ductile iron casting, the tensile strength of the ductile iron casting test piece can be made greater than 400 MPa, the yield strength can be greater than 280 MPa, and the low-temperature impact energy at -20°C can be greater than 7J.

[0070] In addition, the sand casting method of ductile iron castings according to the present invention, combined with the cold iron chilled sand casting method for casting, can improve the comprehensive mechanical properties of the main parts of the wind turbine main shaft, while improving the low-temperature impact energy while still ensuring higher strength (for example, tensile strength and yield strength).

[0071] An object of the present invention is to provide a ductile iron casting method capable of improving the comprehensive mechanical properties of the ductile iron casting.

[0072] Another object of the present invention is to provide an iron mold casting method for ductile iron castings that can improve the structural density of ductile iron castings and reduce the number of shrinkage cavities.

[0073] Another object of the present invention is to provide a ductile iron casting (eg, a main shaft of a wind turbine) and a wind turbine with improved comprehensive mechanical properties.

[0074] According to one aspect of the present invention, a method for casting a ductile iron casting is provided, the method comprising pouring molten iron into a cavity formed by a metal outer mold and a sand core, wherein the ductile iron casting comprises, by mass percentage, C 3.6-3.8wt%, Si 2.3-2.6wt%, Mn ≤ 0.14wt%, and Ni 0.20-0.55wt%.

[0075] Optionally, the iron mold casting method further comprises: (1) smelting: subjecting the material including pig iron to carburization treatment and smelting it into molten iron; (2) spheroidizing and inoculating: subjecting the molten iron obtained from step (1) to spheroidizing and inoculating; and (3) pouring: pouring the molten iron obtained from step (2) into the mold cavity, wherein, in step (1) and / or step (2), the preparation method further comprises microalloying, the microalloying comprising adding Ni, adding a spheroidizing agent containing Si and an inoculant containing Si in step (2), and adding a flow inoculant containing Si in step (3).

[0076] Optionally, based on the total mass of the molten iron, in step (1), the content of Si included in the material is in the range of 1.4-1.6wt%, in step (2), a spheroidizer containing Si and an inoculant containing Si are added so that the content of Si is in the range of 2.25-2.45wt%, and in step (3), a flow inoculant containing Si is added so that the content of Si is in the range of 2.3-2.6wt%.

[0077] Optionally, based on the total mass of the spheroidizer, the spheroidizer includes 40-50 wt% Si by mass percentage, based on the total mass of the inoculant, the inoculant includes 72-78 wt% Si by mass percentage, based on the total mass of the inoculant, the inoculant includes 70-80 wt% Si by mass percentage.

[0078] Optionally, based on the total mass of the inoculant, the inoculant includes, by mass percentage, Si 72-78wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al<1.5wt%, and the rest is iron; based on the total mass of the spheroidizer, the spheroidizer includes, by mass percentage, Mg 4.5-6wt%, RE 0.15-0.3wt%, Si 40-50wt%, and the rest is iron; based on the total mass of the inoculant, the inoculant includes, by mass percentage, Si 70-80wt%, Bi 0.5-2.5wt%, Ca≤2.0wt%, Al≤2.0wt%, and the rest is Fe.

[0079] Optionally, in step (2), the amount of inoculant added is 0.35-0.67wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.0-1.3wt% of the total mass of the molten iron, and in step (3), the amount of inoculant added is 0.08-0.2wt% of the total mass of the molten iron.

[0080] Optionally, the inoculant in step (2) includes a primary inoculant and a covering inoculant, wherein the primary inoculant comprises, by mass percentage, Si 72-78wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al <1.5wt%, and the remainder is iron, based on the total mass of the covering inoculant, the covering inoculant comprises, by mass percentage, Si 72-78wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al <1.5wt%, and the remainder is iron.

[0081] Optionally, in step (2), the amount of the primary inoculant added is 0.30-0.55 wt% of the total mass of the molten iron, and the amount of the covering inoculant added is 0.05-0.12 wt% of the total mass of the molten iron.

[0082] Optionally, Mg is added in step (2) so that the content of Mg is in the range of 0.045-0.078 wt% based on the total mass of the molten iron, the spheroidizing agent includes 4.5-6 wt% of Mg by mass based on the total mass of the spheroidizing agent, the amount of the spheroidizing agent added in step (2) is 1.0-1.3 wt% of the total mass of the molten iron, and in step (1) and / or step (2), the amount of Ni added is 0.2-0.4 wt% of the total mass of the molten iron. The microalloying treatment in step (1) and / or step (2) includes adding Ni so that the content of Ni is in the range of 0.20-0.55 wt% of the total mass of the molten iron. In step (1) and / or step (2), the microalloying treatment further includes adding TiC to the molten iron, and the amount of TiC added is 0.01-0.03 wt% of the total mass of the molten iron.

[0083] Optionally, the pig iron in step (1) is pig iron of grade Q10 or above, and the Mn content in step (1) is adjusted so that the Mn content in step (1) is within the range of 0.10-0.12wt% of the total mass of the molten iron.

[0084] Optionally, the wall thickness of the metal outer mold (110) is 100mm-200mm.

[0085] Optionally, before pouring the molten iron into the cavity, the temperature of the cavity is preheated to 50-200°C. In step (4), the pouring temperature of the molten iron is 1330-1360°C, and the pouring speed of the molten iron is 100-150kg / s.

[0086] Optionally, the content of Si is in the range of 2.30-2.40 wt%.

[0087] According to another aspect of the present invention, there is provided a ductile iron casting, which is formed by the iron mold casting method as described above.

[0088] Optionally, the wall thickness of the ductile iron casting is greater than or equal to 60 mm.

[0089] Optionally, the ductile iron casting is the main shaft of a wind turbine generator set, and the main shaft includes a shaft body, a large flange arranged at one axial end of the shaft body, a trumpet-shaped connecting piece connecting the shaft body and the large flange, and a small flange arranged at the other axial end of the shaft body, and the outer diameter of the shaft body is greater than or equal to 1.0m.

[0090] According to another aspect of the present invention, a wind turbine generator set is provided, comprising the ductile iron casting as described above.

[0091] According to the iron mold casting method of the ductile iron casting of the present invention, the comprehensive mechanical properties of the ductile iron casting can be improved by controlling the composition of the ductile iron casting and / or the iron mold casting method.

[0092] According to the iron mold casting method of the ductile iron casting of the present invention, by controlling the composition of the ductile iron casting, the tensile strength of the ductile iron casting test piece can be made greater than 400 MPa, the yield strength can be made greater than 280 MPa, and the low-temperature impact energy at -20°C can be made greater than 7 J. Therefore, the method can be widely used in the manufacture of ductile iron castings with high comprehensive performance requirements.

[0093] Furthermore, the iron mold casting method for ductile iron castings according to the present invention can improve the comprehensive mechanical properties of key components of wind turbine main shafts, increasing low-temperature impact energy while still maintaining high strength (e.g., tensile strength and yield strength). Therefore, the iron mold casting method for ductile iron castings according to the present invention can be widely applied to large-section castings used in wind turbine generators, as well as castings in other fields that require high comprehensive performance.

[0094] The object of the present invention is to provide a forming method for ductile iron castings, the ductile iron castings and a wind turbine generator set.

[0095] According to an embodiment of the present invention, a method for forming a ductile iron casting is provided. The method comprises: preparing a forming mold, the forming mold comprising an outer mold box and an inner core located in the outer mold box, the outer mold box comprising a metal casting mold and a sand coating layer covering an inner cavity surface of the metal casting mold, and forming a mold cavity between the outer mold box and the inner core; and performing casting, pouring molten iron into the mold cavity, and forming the ductile iron casting after cooling and solidification. The ductile iron casting comprises, by mass percentage, the following: C 3.6-3.8wt%, Si 2.3-2.6wt%, Mn ≤0.14wt%, and Ni 0.20-0.55wt%.

[0096] According to one aspect of an embodiment of the present invention, the ductile iron casting further comprises, by mass percentage: V 0.001-0.01wt%, Ti 0.02-0.03wt%, P≤0.035wt%, S≤0.02wt%, Cr≤0.025wt%, and residual Mg 0.035-0.060wt%.

[0097] According to one aspect of an embodiment of the present invention, the molten iron is prepared by the following method: (1) smelting: subjecting a material including pig iron to carburization treatment and smelting it into molten iron; (2) spheroidizing and inoculating: subjecting the molten iron obtained from step (1) to spheroidizing and inoculating; and (3) pouring: pouring the molten iron obtained from step (2) into the mold cavity, wherein, in step (1) and / or step (2), the preparation method further includes microalloying, the microalloying including adding Ni, adding a spheroidizing agent containing Si and an inoculant containing Si in step (2), and adding a flow inoculant containing Si in step (3).

[0098] According to one aspect of an embodiment of the present invention, in step (1), the content of Si included in the material is in the range of 1.4-1.6 wt%, in step (2), a spheroidizer containing Si and an inoculant containing Si are added so that the content of Si is in the range of 2.25-2.45 wt%, and in step (3), a flow-in-place inoculant containing Si is added so that the content of Si is in the range of 2.3-2.6 wt%.

[0099] According to one aspect of an embodiment of the present invention, the spheroidizer includes 40-50 wt % of Si by mass based on the total mass of the spheroidizer, the inoculant includes 72-78 wt % of Si by mass based on the total mass of the inoculant, and the inoculant includes 70-80 wt % of Si by mass based on the total mass of the inoculant.

[0100] According to one aspect of an embodiment of the present invention, based on the total mass of the inoculant, the inoculant includes, by mass percentage, Si 72-78wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al<1.5wt%, and the remainder is iron; based on the total mass of the spheroidizer, the spheroidizer includes, by mass percentage, Mg 4.5-6wt%, RE 0.15-0.3wt%, Si 40-50wt%, and the remainder is iron; based on the total mass of the inoculant, the inoculant includes, by mass percentage, Si 70-80wt%, Bi 0.5-2.5wt%, Ca≤2.0wt%, Al≤2.0wt%, and the remainder is Fe.

[0101] According to one aspect of an embodiment of the present invention, in step (2), the amount of inoculant added is 0.35-0.67wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.0-1.3wt% of the total mass of the molten iron, and in step (3), the amount of inoculant added is 0.08-0.2wt% of the total mass of the molten iron.

[0102] According to one aspect of an embodiment of the present invention, the inoculant in step (2) includes a primary inoculant and a covering inoculant. Based on the total mass of the primary inoculant, the primary inoculant includes, by mass percentage, Si 72-78wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al <1.5wt%, and the remainder is iron. Based on the total mass of the covering inoculant, the covering inoculant includes, by mass percentage, Si 72-78wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al <1.5wt%, and the remainder is iron.

[0103] According to one aspect of an embodiment of the present invention, in step (2), the amount of the primary inoculant added is 0.30-0.55 wt% of the total mass of the molten iron, and the amount of the covering inoculant added is 0.05-0.12 wt% of the total mass of the molten iron.

[0104] According to one aspect of an embodiment of the present invention, Mg is added in step (2) so that the content of Mg is in the range of 0.045-0.078 wt% based on the total mass of the molten iron, the spheroidizing agent includes 4.5-6 wt% of Mg in terms of mass percentage based on the total mass of the spheroidizing agent, the amount of the spheroidizing agent added in step (2) is 1.0-1.3 wt% of the total mass of the molten iron, and in step (1) and / or step (2), the amount of Ni added is 0.2-0.4 wt% of the total mass of the molten iron. The microalloying treatment in step (1) and / or step (2) includes adding Ni so that the content of Ni is in the range of 0.20-0.55 wt% of the total mass of the molten iron, and in step (1) and / or step (2), the microalloying treatment further includes adding TiC to the molten iron, and the amount of TiC added is 0.01-0.03 wt% of the total mass of the molten iron.

[0105] According to one aspect of an embodiment of the present invention, the pig iron in step (1) is pig iron of grade Q10 or above, and the content of Mn is adjusted in step (1) so that the content of Mn in step (1) is in the range of 0.10-0.12wt% of the total mass of the molten iron.

[0106] According to one aspect of an embodiment of the present invention, before pouring molten iron into the mold cavity (130), the temperature of the mold cavity (130) is preheated to 50-200°C. In step (4), the pouring temperature of the molten iron is 1330-1360°C, and the pouring speed of the molten iron is 100-150kg / s.

[0107] According to one aspect of an embodiment of the present invention, the metal casting mold is an iron mold, the thickness of the iron mold is 50 mm-200 mm, and the thickness of the sand coating layer is 6 mm-20 mm.

[0108] According to one aspect of an embodiment of the present invention, the outer mold box includes a bottom box, a top box, and a middle box arranged between the bottom box and the top box, the middle box is an iron mold covered sand mold box, the top box and the bottom box are sand boxes, and the inner core is a sand core.

[0109] According to one aspect of an embodiment of the present invention, the forming mold further includes a bottom pouring system, and a runner for conveying molten iron into the mold cavity is provided in the bottom box.

[0110] According to one aspect of the embodiment of the present invention, a riser is provided in the top box, and an exhaust channel is provided in the inner core, and the exhaust channel is communicated with the riser.

[0111] According to one aspect of the embodiments of the present invention, the matrix of the ductile iron is ferrite.

[0112] According to one aspect of an embodiment of the present invention, the ductile iron casting is a main shaft of a wind turbine generator set, and in the axial direction of the main shaft, the outer mold box and / or the inner mold core is divided into multiple sections.

[0113] According to another aspect of an embodiment of the present invention, a ductile iron casting is provided. The ductile iron casting is manufactured by the aforementioned molding method.

[0114] According to another aspect of the embodiment of the present invention, the wall thickness of the ductile iron casting is greater than or equal to 60 mm.

[0115] According to another aspect of the embodiment of the present invention, the ductile iron casting is a main shaft of a wind turbine generator set, and the outer diameter of the main shaft is greater than or equal to 1 meter.

[0116] According to another aspect of the embodiments of the present invention, a wind turbine generator set is provided, wherein the wind turbine generator set includes the ductile iron casting described above.

[0117] The core structure of the ductile iron casting obtained by the ductile iron forming method according to the embodiment of the present invention is good, and there is basically no special-shaped graphite such as fragmented graphite, and the comprehensive performance is excellent. In particular, the tensile strength of the ductile iron test block is greater than 400MPa, the yield strength is greater than 280MPa, and the low-temperature impact energy at -20°C is greater than 7J, which significantly improves the mechanical properties of large-section ductile iron. Therefore, the high-toughness, ultra-high-strength ferritic ductile iron provided by the present invention is particularly suitable for mass production of key components such as large-section castings in wind turbines, especially it can significantly improve the low-temperature impact energy, ensure the low-temperature strength of the components, and reduce the risk of component fracture. BRIEF DESCRIPTION OF THE DRAWINGS

[0118] The above and other objects and features of the present invention will become more apparent through the following description with reference to the accompanying drawings which exemplarily illustrate embodiments of the present invention, in which:

[0119] FIG1 is a main shaft of a wind turbine generator set as an example of a ductile iron casting;

[0120] FIG2 is an axial cross-sectional view of FIG1 ;

[0121] 3 is a schematic diagram of a sand mold for preparing ductile iron castings according to an embodiment of the present invention;

[0122] FIG4 is a perspective view of a gating system for a spindle according to an embodiment of the present invention;

[0123] FIG5 is an axial cross-sectional view of FIG4;

[0124] 6 is a perspective view of a pouring system for a main shaft according to another embodiment of the present invention;

[0125] FIG7 is an axial cross-sectional view of FIG6;

[0126] FIG8 is a perspective view of a fan main shaft according to an embodiment of the present invention;

[0127] FIG9 is a cross-sectional view of a main shaft of a fan according to an embodiment of the present invention;

[0128] FIG10 is a cross-sectional view of a molding die according to an embodiment of the present invention;

[0129] 11 is a cross-sectional view of another example of a molding die according to an embodiment of the present invention;

[0130] 12 is a schematic diagram of a sand-shooting process of a molding die according to an embodiment of the present invention;

[0131] 13A and 13B respectively show the graphite morphology of ductile iron according to a comparative example and an inventive example;

[0132] 14A and 14B respectively show the tensile fracture morphologies of ductile iron according to a comparative example and an inventive example;

[0133] 15A and 15B respectively show the three-dimensional morphology of the tensile fracture of ductile iron according to the comparative example and the inventive example; and

[0134] 16A and 16B show the impact fracture morphologies of ductile iron according to a comparative example and an inventive example, respectively. DETAILED DESCRIPTION

[0135] In the following description, for the purpose of explanation, numerous specific details are set forth to provide a thorough understanding of the various embodiments or implementations of the invention. As used herein, "embodiment" and "implementation" are interchangeable terms and are non-limiting examples of devices or methods that employ one or more of the inventive concepts disclosed herein. However, it is apparent that the various embodiments can be practiced without these specific details or with one or more equivalent arrangements. Furthermore, the various embodiments may be different, but are not necessarily exclusive.

[0136] It should be understood that when the terms "include" and / or "comprises" are used in the specification, they list the presence of stated materials and / or components, but do not preclude the presence or addition of one or more other materials and / or components.

[0137] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure is a part. Terms (such as those defined in common dictionaries) should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined as such herein.

[0138] The present invention provides ductile iron, which may include, by mass percentage, the following: C 3.6-3.8wt%, Si 2.3-2.6wt%, Mn≤0.14wt%, and Ni 0.20-0.55wt%, based on the total mass of the ductile iron. Furthermore, the matrix of the ductile iron according to an embodiment of the present invention may be ferrite.

[0139] The present invention controls the content of various elements in ductile iron, especially the content of Si, Mn and Ni, thereby achieving the technical effects of a tensile strength greater than 400 MPa, a yield strength greater than 280 MPa, and a low-temperature impact energy greater than 7 J at -20°C.

[0140] In an embodiment, the ductile iron according to the exemplary embodiment of the present invention may further include, by mass percentage: V 0.001-0.01wt%, Ti 0.02-0.03wt%. In another embodiment, the ductile iron according to the exemplary embodiment of the present invention may further include, by mass percentage: P≤0.035wt%, S≤0.02wt%, Cr≤0.025wt%, Mg≤0.035wt%, S≤0.02wt%, Cr≤0.025wt%, Mg≤0.035wt%, Mg ...35wt%, Mg≤0.025wt%, Mg≤0.035wt%, 残 0.035-0.060wt%.

[0141] Specifically, Si can play a role in solid solution strengthening. The principle is to form a solid solution by incorporating a certain solute element into the molten iron, thereby strengthening the metal. The solute atoms incorporated into the solid solution cause lattice distortion, which increases the resistance to dislocation movement, making slip difficult, thereby increasing the strength and hardness of the alloy solid solution. When the concentration of solute atoms in the melt is moderate, the strength and hardness of the material are significantly improved, but its toughness and plasticity are reduced. In an embodiment of the present invention, the Si content can be controlled within the range of 2.3-2.6wt%, preferably within the range of 2.30-2.49wt%, within the range of 2.35-2.49wt%, or within the range of 2.30-2.40wt%, more preferably within the range of 2.39-2.45wt%. If the Si content is outside the range defined by the present invention, the toughness and plasticity of ductile iron will decrease, so the Si content must be strictly controlled.

[0142] Mn is a positive segregation element that easily forms alloy carbides at grain boundaries, stabilizes pearlite, and inhibits the formation of ferrite. Mn will significantly increase the ductile-brittle transition temperature and reduce the plasticity and toughness of ductile iron. For every 0.1% increase in manganese, the low-temperature brittle transition temperature of ductile iron will increase by 12°C. In order to ensure the low-temperature impact toughness of ductile iron, the Mn content must be strictly controlled. In an embodiment of the present invention, the Mn content can be controlled in a range of less than or equal to 0.14wt%, preferably in the range of 0.10-0.12wt%. If the Mn content is outside the range defined by the present invention, the ductile-brittle transition temperature will increase, which will lead to a decrease in low-temperature impact performance.

[0143] Ni can be infinitely dissolved in ductile iron without affecting the graphite morphology and the number of eutectic cells. Nickel in the cast state can promote the formation of pearlite and refine pearlite, and has a certain solid solution strengthening effect on ferrite, which is beneficial to improving the tensile strength of ductile iron, but it will reduce the elongation and low-temperature impact toughness of ductile iron. Adding nickel to low-temperature high-toughness ductile iron cannot effectively reduce the toughness-brittle transition temperature, and the effect of nickel on improving the low-temperature impact toughness of the material is not obvious, but it can improve its tensile strength without reducing the low-temperature impact toughness of the material, thereby compensating for the problem of insufficient strength caused by the reduction of silicon content. In an embodiment of the present invention, the Ni content can be controlled within the range of 0.20-0.55wt%, preferably within the range of 0.35-0.55wt%, and more preferably within the range of 0.35-0.45wt%. If the Ni content is outside the range defined by the present invention, the strength and hardness of the ductile iron will deteriorate, so the Ni content must be strictly controlled.

[0144] Excessive Ti and Cr contents will have an adverse effect on the structure and properties of ductile iron. Ti and Cr are both very active elements, and they easily produce particles with very high microhardness with C and N. Ti and Cr also have the characteristics of selective crystallization, and they tend to be enriched at the grain boundaries and the final solidification area of ​​the casting during the crystallization process. Excessive Ti and Cr contents will affect the quality of spheroidization, interfere with spheroidization, and cause the shape of graphite to be distorted. Therefore, preferably, the content of Ti and Cr can be controlled to further improve the performance of ductile iron. In an embodiment of the present invention, preferably, the Ti content can be in the range of 0.02-0.03wt%, and the Cr content can be less than or equal to 0.025wt%.

[0145] S and Mg 残It is one of the reasons for the formation of grain boundary inclusions, the reduction of impact performance, and the low-temperature impact performance. Therefore, in order to further improve the performance of ductile iron, its content can be controlled within a relatively low range. In addition, Mg can also promote the spheroidization of graphite, making the spheroidization rate of graphite higher and the distribution more uniform. In the embodiment of the present invention, preferably, the S content can be controlled within the range of less than or equal to 0.02wt%, more preferably, less than 0.015wt%. Preferably, Mg can be 残 The content of is controlled in the range of 0.035-0.060 wt %, more preferably, in the range of 0.040-0.054 wt %.

[0146] P is one of the elements that affects the ductile-brittle transition temperature of ductile iron. Therefore, in order to further improve the performance of ductile iron, the content of P can be controlled. In the embodiment of the present invention, the content of P can be preferably controlled within a range of less than or equal to 0.035 wt%.

[0147] In embodiments of the present invention, the mechanical properties of the ductile iron of the present invention can be further improved by utilizing V's solid solution strengthening in the ductile iron, its precipitation phases during solidification, the compounds formed, and its matrix strengthening effects. Therefore, the V content can preferably be controlled within the range of 0.001-0.01 wt%.

[0148] In the ductile iron of the embodiment of the present invention, the content of Si is controlled within the range of 2.3-2.6wt%, the content of Mn is controlled within the range of less than or equal to 0.14wt%, the content of Ni is controlled within the range of 0.20-0.55wt%, and more preferably, the content of V is also controlled within the range of 0.001-0.01wt%, and the content of Ti is also controlled within the range of 0.02-0.03wt%. Therefore, the ductile iron of the embodiment of the present invention can obtain a tensile strength greater than 400MPa, a yield strength greater than 280MPa, and a low-temperature impact energy greater than 7J at -20°C. The relevant technical effect can refer to the performance of the casting reaching the relevant index, or the effect of the test block reaching the relevant index. The test block can be a test block prepared according to the standard GB_T 1348-2019 ductile iron casting, or a test block that can reflect the performance of the overall casting. In other words, the ductile iron of the present invention can satisfy the impact energy greater than 7J at -20°C while maintaining the existing strength.

[0149] Therefore, the ductile iron of the present invention can be widely used in castings, especially castings in wind turbine generator sets.

[0150] Hereinafter, a method for preparing ductile iron according to an embodiment of the present invention will be described in detail.

[0151] The method for preparing ductile iron according to an embodiment of the present invention may include the following steps:

[0152] (1) Smelting: Carburizing materials including pig iron and smelting them into molten iron;

[0153] (2) Spheroidizing and inoculating: spheroidizing and inoculating the molten iron obtained from step (1); and

[0154] (3) Pouring: pouring the molten iron obtained from step (2),

[0155] Wherein, in step (1) and / or step (2), the method for preparing ductile iron according to an embodiment of the present invention may further include microalloying.

[0156] Specifically, in step (1) and / or step (2), the microalloying treatment may include adding Ni so that the Ni content is 0.20-0.55 wt% based on the total mass of the molten iron. A spheroidizing agent containing Si and an inoculant containing Si may be added in step (2), and a stream inoculant containing Si may be added in step (3), so that the Si content is 2.3-2.6 wt% based on the total mass of the molten iron. The materials charged to the furnace in step (1) may be adjusted so that the Mn content is less than or equal to 0.14 wt% based on the total mass of the molten iron.

[0157] In the present invention, the amount of additives (e.g., carburizer, spheroidizer, inoculant, etc.) added in each step is much less than the total mass of the molten iron in each step. Therefore, the amount of additives added in each step can be ignored with respect to the total mass of the molten iron. That is, the total mass of the molten iron in each step of the present invention is substantially equal. In other words, the "total mass of the molten iron" in the present invention may refer to the mass of the molten iron obtained by melting the materials including the pig iron in step (1).

[0158] In addition, the preparation method of ductile iron according to an embodiment of the present invention can control the content of Si, Mn and / or Ni in different steps to further improve the comprehensive properties of ductile iron (for example, improving tensile strength, yield strength greater than and low-temperature impact energy).

[0159] The present invention controls the content of Ni in the molten iron to be within the range of 0.20-0.55 wt%, preferably 0.35-0.55 wt%, and more preferably 0.35-0.45 wt%, based on the total mass of the molten iron, by adding Ni through microalloying in step (1) and / or step (2). Furthermore, the present invention controls the content of Si in the molten iron to be within the range of 1.4-1.6 wt%, by adding a spheroidizing agent and an inoculant containing Si in step (2) to control the content of Si to be within the range of 2.25-2.45 wt%, based on the total mass of the molten iron, and by adding a Si-containing inoculant in step (4) to control the content of Si to be within the range of 2.3-2.6 wt%, preferably 2.35-2.49 wt%, 2.30-2.10 wt%, and more preferably 2.39-2.45 wt%, based on the total mass of the molten iron. In addition, the present invention adjusts the Mn content in step (1) to control the Mn content based on the total mass of the molten iron to be less than or equal to 0.14wt%, preferably within the range of 0.10-0.12wt%.

[0160] Specifically, in step (1), a material including pig iron can be added to a smelting furnace and heated to melt, so that the material is smelted into molten iron. Pig iron, recycled materials, and scrap steel commonly used in the art can be used, as long as the Si content in step (1) is within the range of 1.4-1.6 wt% based on the total mass of the molten iron and the Mn content is less than or equal to 0.14 wt% based on the total mass of the molten iron. For example, the pig iron in the present invention can include pig iron of grades Q10 and above. However, the embodiments of the present invention are not limited thereto.

[0161] In addition, in step (1), if the Si content is lower than 1.4wt%, ferrosilicon with a higher Si content needs to be added. If the Si content is higher than 1.6wt%, other pig iron with a lower Si content (such as plain carbon steel, but the present invention is not limited thereto) needs to be added. In addition, in step (1), the Mn content is preferably controlled within the range of 0.10-0.12wt%. If the Mn content of the molten iron in step (1) is low, ferromanganese can be added to increase the Mn content in the molten iron. However, the embodiments of the present invention are not limited thereto.

[0162] In step (1), the molten iron obtained by smelting can be subjected to a carburizing treatment. Specifically, a carburizer can be added to the molten iron to perform the carburizing treatment on the molten iron. For example, the temperature of the molten iron can be controlled within the range of 1400°C-1450°C, and the carburizer can be added to the molten iron to perform the carburizing treatment. In an embodiment of the present invention, in order to reduce the influence of trace elements on ductile iron, the carbon content in the carburizer can be greater than 90wt% and the sulfur content can be less than 0.05wt%. Under the guidance of the concept of the present invention, those skilled in the art can select a suitable carburizer as long as it meets the above conditions.

[0163] In step (2), the molten iron obtained in step (1) can be subjected to spheroidization, inoculation, and microalloying. Specifically, as an example, an inoculant can be first laid on one side of the dam in the spheroidizing bag, and then a spheroidizing agent and a microalloy can be laid on the other side of the dam in the spheroidizing bag and covered with iron filings. Then, the molten iron after the carburization treatment is added to the spheroidizing bag, thereby performing the spheroidization, inoculation, and microalloying process. Optionally, the molten iron can also be subjected to microalloying in step (1).

[0164] In step (3), a flow-inoculating agent is added during the pouring of the molten iron obtained from step (2) to perform flow-inoculation.

[0165] In an embodiment of the present invention, the spheroidizer may include 40-50 wt% Si by mass based on the total mass of the spheroidizer. Preferably, the spheroidizer may include, by mass, 4.5-6 wt% Mg, 0.15-0.3 wt% RE, 40-50 wt% Si, with the remainder being iron. However, the embodiments of the present invention are not limited thereto. Based on the total mass of the inoculant, the inoculant may include, by mass, 75±3 wt% Si. Preferably, the inoculant may include, by mass, 75±3 wt% Si, 1.0-2.0 wt% Ca, 2.0-3.0 wt% Ba, <1.5 wt% Al, with the remainder being iron. However, the embodiments of the present invention are not limited thereto. In addition, in step (2), the amount of inoculant added can be 0.35-0.67wt% of the total mass of the molten iron, and the amount of spheroidizer added can be 1.0-1.3wt% of the total mass of the molten iron, so as to control Si in step (2) within the range of 2.25-2.45wt% based on the total mass of the molten iron.

[0166] In an embodiment of the present invention, based on the total mass of the flow inoculant, the flow inoculant may include 70-80wt% Si by mass percentage. Preferably, the flow inoculant may include: Si 70-80wt%, Bi 0.5-2.5wt%, Ca≤2.0wt%, Al≤2.0wt%, and the rest is Fe. However, the embodiment of the present invention is not limited thereto. In step (3), the amount of the flow inoculant added may be 0.08-0.2wt% of the total mass of the molten iron to control the Si content based on the total mass of the molten iron to be within the range of 2.3-2.6wt%.

[0167] In a preferred embodiment, the inoculant in step (2) may include a primary inoculant and a covering inoculant. In an embodiment, based on the total mass of the primary inoculant, the primary inoculant may include 75±3wt% of Si by mass percentage. Preferably, the primary inoculant may include, by mass percentage, the following: Si 75±3wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al<1.5wt%, and the remainder is iron. In an embodiment, based on the total mass of the covering inoculant, the covering inoculant may include 75±3wt% of Si by mass percentage. Preferably, the covering inoculant may include, by mass percentage, the following: Si 75±3wt%, Ca 1.0-2.0wt%, Ba 2.0-3.0wt%, Al<1.5wt%, and the remainder is iron.

[0168] Specifically, as an example, a primary inoculant can be laid on one side of a dam within a spheroidizing ladle, while a spheroidizing agent, a microalloy, and a covering inoculant can be laid on the other side, and the spheroidizing agent and microalloy can be covered with iron filings. Subsequently, the carburized molten iron can be added to the spheroidizing ladle. In an embodiment, the primary inoculant can be added in an amount of 0.30-0.55 wt% of the total mass of the molten iron, the spheroidizing agent can be added in an amount of 1.0-1.3 wt% of the total mass of the molten iron, the covering inoculant can be added in an amount of 0.05-0.12 wt% of the total mass of the molten iron, and the inoculant can be added in an amount of 0.08-0.20 wt% of the total mass of the molten iron. However, embodiments of the present invention are not limited thereto, as long as the Si content based on the total mass of the ductile iron is within the range of 2.3-2.6 wt%. More preferably, the Si content in step (1) is within the range of 1.4-1.6 wt%, the Si content in step (2) is within the range of 2.25-2.45 wt%, and the Si content in step (3) is within the range of 2.3-2.6 wt%.

[0169] In an embodiment, Mg may be added in step (2) such that the content of Mg is in the range of 0.045-0.078 wt% based on the total mass of the molten iron. In an embodiment, Mg may be included in the spheroidizing agent. Based on the total mass of the spheroidizing agent, the spheroidizing agent may include 4.5-6.5 wt% of Mg by mass percentage, and the amount of the spheroidizing agent added in step (2) may be 1.0-1.3 wt% of the total mass of the molten iron. However, embodiments of the present invention are not limited thereto.

[0170] In step (1) and / or step (2), the microalloying treatment may include adding Ni to control the Ni content based on the total mass of the molten iron to be within the range of 0.20-0.55 wt %. Specifically, the amount of Ni added may be 0.20-0.40 wt % of the total mass of the molten iron.

[0171] In another embodiment, in step (1) and / or step (2), the microalloying process may further include adding TiC to the molten iron, wherein the amount of TiC added may be 0.01-0.03 wt% of the total mass of the molten iron. In some preferred embodiments, a carrier may be added to the TiC, wherein the carrier is 75% ferrosilicon. The mixture of TiC and 75% ferrosilicon can uniformly distribute the alloy components at the grain boundaries, thereby achieving a solid solution strengthening effect. Preferably, the mass ratio of TiC to 75% ferrosilicon may be 1:2.

[0172] In step (3), a flow-in-place inoculant is added to the molten iron obtained from step (2) and poured. The amount of the flow-in-place inoculant added can be 0.1-0.2 wt% of the total mass of the molten iron.

[0173] The pouring temperature in step (3) may be 1330-1360° C. In an embodiment, step (3) further comprises slowly cooling the casting to below 400° C. after pouring, wherein the slow cooling rate may be 10-20° C. / min.

[0174] The present invention controls the contents of Si, Mn, and Ni, more preferably, controls the contents of Si and Mn in step (1), controls the content of Ni in step (1) and / or (2), and controls the content of Si in steps (2) and (3), respectively, to obtain ductile iron having a tensile strength greater than 400 MPa, a yield strength greater than 280 MPa, and a low-temperature impact energy greater than 7 J at -20°C. Specifically, in step (1), the content of Si is controlled to be 1.4-1.6 wt%, and the content of Mn is controlled to be less than or equal to 0.14 wt%. In step (1) and / or step (2), the content of Ni is controlled to be 0.20-0.55 wt% by microalloying. In step (2), a spheroidizing agent and an inoculant are added to control the content of Si to be 2.25-2.45 wt%. In step (3), a stream-inoculating agent is added to control the content of Si to be 2.3-2.6 wt%.

[0175] In the prior art, for small parts (e.g., with a wall thickness of less than 60 mm), good heat dissipation and rapid solidification allow for a relatively short graphite growth period, resulting in a low tendency for graphite distortion, easy microstructure control, and excellent material properties. However, for large-section castings, the cooling rate is slow, leading to a long growth period for graphite nodules. Furthermore, since the material is strengthened by silicon solid solution and has a high silicon content, large-section castings often exhibit deformed graphite, such as fragmented graphite, and their performance deteriorates dramatically. The ductile iron prepared by the present invention solves these problems, achieving a good core microstructure with virtually no fragmented graphite, such as deformed graphite, making it particularly suitable for large-section castings.

[0176] Hereinafter, a sand casting method for a ductile iron casting, a ductile iron casting, a main shaft of a wind turbine generator set, and a wind turbine generator set according to embodiments of the present invention will be described with reference to Figures 1 to 7. Figure 1 illustrates a main shaft of a wind turbine generator set as an example of a ductile iron casting, Figure 2 is an axial cross-sectional view of Figure 1, Figure 3 is a schematic diagram of a sand mold for producing a ductile iron casting according to an embodiment of the present invention, Figure 4 is a perspective view of a gating system for a main shaft according to one embodiment of the present invention, Figure 5 is an axial cross-sectional view of Figure 4, Figure 6 is a perspective view of a gating system for a main shaft according to another embodiment of the present invention, and Figure 7 is an axial cross-sectional view of Figure 6.

[0177] The sand casting method of the ductile iron casting according to the embodiment of the present invention may include: preparing a mold; preparing a sand mold 100, using the mold to prepare the sand mold 100, the sand mold 100 including a cavity 130; pouring molding, pouring molten iron into the cavity 130, and forming the ductile iron casting after cooling and solidification.

[0178] Ductile iron castings according to embodiments of the present invention can be formed using sand casting. These castings can be used for the main shaft of a large-section wind turbine generator set, as well as for the planetary carrier of a gearbox for such a large-section wind turbine generator set. Furthermore, these castings are not limited to components in the wind power generation field and can also be used for other types of castings. For example, the wall thickness of the castings can be greater than or equal to 60 mm.

[0179] For the convenience of description, the sand casting method of ductile iron castings will be described in detail below by taking the ductile iron castings as the main shaft of a wind turbine generator set as an example.

[0180] As shown in Figures 1 and 2, one end of the main shaft 20 (the left end in Figure 1) is used to connect to the impeller of the wind turbine generator set, and the other end of the main shaft 20 (the right end in Figure 1) is used to connect to the gearbox of the wind turbine generator set. The main shaft 20 includes a shaft body 21, a large flange 22 provided at one end of the main shaft 20, and a trumpet-shaped connector 23 connecting the shaft body 21 and the large flange 22. In addition, the main shaft 20 also includes a small flange 24 provided at the other end of the main shaft 20. The large flange 22 is provided at the radially large end of the main shaft 20 and is used to connect to the impeller of the wind turbine generator set. The small flange 24 is provided at the radially small end of the main shaft 20 and is used to connect to the gearbox of the wind turbine generator set. The large flange 22, trumpet-shaped connector 23, and small flange 24 are used to connect to other rotating components and are subject to large and complex loads, requiring guaranteed comprehensive mechanical properties. According to an embodiment of the present invention, specifically, the outer diameter of the shaft body 21 can be greater than or equal to 1m.

[0181] A mold (not shown) may be used to prepare the sand mold 100. When the ductile iron casting is the main shaft 20, the mold may include an outer mold and an inner sand core 120 described later.

[0182] As shown in FIG3 , the sand mold 100 may include an outer sand mold 110 and an inner sand core 120 , which enclose a molding cavity 130. The outer shape of the outer sand mold 110 is determined by the inner shape of the flask and is not particularly limited. The inner shape of the outer sand mold 110 may be determined by an outer mold and conform to the outer shape of the spindle 20 . The outer shape of the inner sand core 120 conforms to the inner shape of the spindle 20 . As desired, the outer sand mold 110 and inner sand core 120 may be axially divided into multiple sections. For example, the outer sand mold 110 may be axially divided into at least three sections, and the inner sand core 120 may be axially divided into at least two sections, to facilitate manufacturing.

[0183] According to an embodiment of the present invention, the mold cavity 130 may include an axial cavity 131 for forming the shaft body 21, a large flange cavity 132 for forming the large flange 22, a trumpet cavity 133 for forming the trumpet-shaped connector 23, and a small flange cavity 134 for forming the small flange 24. The above division of the mold cavity 130 is a functional division and does not represent a physical division of the structure.

[0184] According to an embodiment of the present invention, the sand mold 100 may further include an external chill 141 and / or an internal chill 142. The external chill 141 is disposed in the outer sand mold 110 around the mold cavity 130 and is exposed from the mold cavity 130. The internal chill 142 is disposed in the inner sand core 120 around the mold cavity 130 and is exposed from the mold cavity 130. According to an embodiment of the present invention, by disposing the external chill 141 and / or the internal chill 142 at key locations, the structural density of the spindle 20 can be increased through strong quenching, thereby improving the overall mechanical properties.

[0185] According to an embodiment of the present invention, the chilling effect can be enhanced by controlling the ratio of the thickness of the chill to the thickness of the corresponding portion of the ductile iron casting. For example, the ratio of the thickness of the outer chill 141 and / or the inner chill 142 to the thickness of the portion of the ductile iron casting overlying the outer chill 141 and / or the inner chill 142 is 0.5-1.5. For example, the ratio is 0.5-1.0.

[0186] According to an embodiment of the present invention, as shown in Figures 4 and 5, the external chill 141 may include a first shaped chill 141a and a second shaped chill 141b. The first shaped chill 141a is disposed at a position corresponding to the upper end surface of the large flange 22 and the outer circumference of the trumpet-shaped connector 23, and the second shaped chill 141b may be disposed at a position corresponding to the lower end surface of the large flange 22.

[0187] As shown in Figure 4, each of the first and second formed chills 141a, 141b surrounds the die cavity 130 in at least two segments, for example, three, four, or more segments. The upper limit of the number of segments in each of the first and second formed chills 141a, 141b is not specifically limited; for example, it may be less than or equal to 10 segments. By arranging the first and second formed chills 141a, 141b in segments, their versatility can be improved. That is, when producing spindles of different sizes, the number of formed chills can be adjusted to ensure that they surround the entire die cavity 130.

[0188] A predetermined spacing can be formed between adjacent first-shaped chills 141a, and a predetermined spacing can also be formed between adjacent second-shaped chills 141b. By reducing the spacing between adjacent first-shaped chills 141a and the number of segments of the first-shaped chill 141a, the coverage of the first-shaped chill 141a can be increased, thereby enhancing the chilling effect. Similarly, by reducing the spacing between adjacent second-shaped chills 141b and the number of segments of the second-shaped chill 141b, the coverage of the second-shaped chill 141b can be increased, thereby enhancing the chilling effect. In other words, compared to using small pieces of chill to cover the flared connector 23 and the large flange 22, the first-shaped chill 141a and the second-shaped chill 141b make it easier to adjust the coverage, thereby enhancing the chilling effect.

[0189] As shown in FIG4 and FIG5, along the axial direction of the main shaft 20, each section of the first formed chill 141a is integrally formed on the outer peripheral surface of the trumpet-shaped connector 23 and the upper end surface of the large flange 22, thereby facilitating the improvement of the chilling effect.

[0190] According to an embodiment of the present invention, the thickness of each of the first and second formed chills 141a and 141b is greater than or equal to 200 mm. According to an embodiment of the present invention, preferably, the thickness of each of the first and second formed chills 141a and 141b is greater than or equal to 230 mm.

[0191] As shown in Figure 5, the main shaft 20 has relatively thick flange 22 and trumpet-shaped connector 23. These are the locations where the main shaft 20 connects to the impeller and are subject to large and complex loads. Therefore, high structural density is required to improve overall mechanical properties. According to an embodiment of the present invention, by ensuring that the thickness of each of the first and second formed chills 141a, 141b is greater than or equal to 200 mm, the cooling rate of the molten iron can be effectively increased, grain size can be refined, and structural density can be improved.

[0192] According to an embodiment of the present invention, the coverage of the first formed chill 141a can be greater than or equal to 90%, and the coverage of the second formed chill 141b can be greater than or equal to 80%. Coverage refers to the ratio of the area covered by the first formed chill 141a or the second formed chill 141b around the mold cavity 130. According to the present invention, by ensuring that the coverage of the first formed chill 141a is greater than or equal to 90% or the coverage of the second formed chill 141b is greater than or equal to 80%, the cooling rate of the molten iron can be effectively increased, the grain size can be refined, and the microstructure can be improved.

[0193] As shown in Figures 4 and 5, the external chill 141 can also be provided at a position corresponding to the outer circumference of the shaft body 21 and the outer circumference of the small flange 24. The external chill 141 provided at this position can be a small piece of chill and is provided around the outer circumference of the shaft body 21 and the small flange 24. However, the present invention is not limited to this, and at least a portion of the external chill 141 surrounding the shaft body 21 and the small flange 24 can also be formed as a large piece of shaped chill. As an example, the thickness of the external chill 141 surrounding the shaft body 21 and the small flange 24 can be less than the thickness of the first shaped chill 141a and the second shaped chill 141b, for example, greater than or equal to 70 mm, or greater than or equal to 100 mm.

[0194] Although not shown, according to an embodiment of the present invention, an external chill 141 may be further provided at a position corresponding to the upper end surface of the small flange 24 to enhance the chilling effect of the small flange 24. The thickness of the external chill 141 provided at a position corresponding to the upper end surface of the small flange 24 may be smaller than the thickness of the first and second formed chills 141a, 141b, and may be, for example, greater than or equal to 100 mm.

[0195] 5 , the internal chill 142 may be provided at a position corresponding to the inner circumference of the trumpet-shaped connector 23. Furthermore, although not shown, the internal chill 142 may also be provided at a position corresponding to the inner end surface of the small flange 24.

[0196] According to an embodiment of the present invention, the sand mold 100 may further include a riser. As shown in FIG. 4 to FIG. 7 , the riser may include at least one of a top riser 151 , a middle riser 152 , and a heat-generating riser 153 .

[0197] The top riser 151 can be a distinct riser, located at a position corresponding to the outer end of the small flange 24, and is used for heat preservation, slag removal, and exhaust. The specific structure and number of the top riser 151 are not limited, and any riser type known in the art can be used. As an example, an air outlet 161 can also be provided on the top riser 151 for exhaust.

[0198] As shown in Figure 4, the middle section riser 152 can be set at a position corresponding to the outer wall of the shaft body 21. The middle section riser 152 is a blind riser. As shown in Figure 4, the blind riser is set at a position of the shaft body 21 where the external chill 141 is not set. At the position where the external chill 141 is set, the molten iron cools rapidly, but there is a tendency for shrinkage at the position where the external chill 141 is not set. Therefore, the middle section riser 152 is set at the position where the external chill 141 is not set to compensate for shrinkage, thereby improving the structural density of the main shaft 20. However, the present invention is not limited to this. As shown in Figure 6, the middle section riser 152 may not be set, but the external chill 141 may be completely covered at the position corresponding to the shaft body 21. The specific structure and number of the middle section riser 152 are not limited.

[0199] As shown in Figures 5 and 7, a heat-generating riser 153 can be positioned corresponding to the inner cavity of the trumpet-shaped connector 23. The specific structure and number of heat-generating risers 153 are not limited. The material of the heat-generating riser 153 can be ignited during the pouring of molten iron. The heat released increases the temperature of the molten iron within the riser, prolonging the solidification time of the molten iron within the riser, extending the feeding time, and improving the feeding efficiency of the riser for the casting.

[0200] According to an embodiment of the present invention, the pouring system of molten iron may be a bottom pouring pouring system. The structure of the bottom pouring pouring system is not limited. As an example, as shown in Figures 4 and 5, the pouring system may include a sprue 171, a disc cavity 172 connected to the sprue 171, a runner 173 connected to the disc cavity 172, and an inner runner 174 connected to the runner 173 and the cavity 130. The sprue 171 may be external, that is, it is arranged on the outside of the sand mold 100 and extends to communicate with the disc cavity 172. As an example, as shown in Figures 6 and 7, the sprue 171 may be internal, that is, it is arranged to pass through the sand core 120 and extend to communicate with the disc cavity 172.

[0201] The ductile iron casting of the present invention can be widely used in castings, especially castings in wind turbine generator sets.

[0202] In addition, according to the present invention, by utilizing a sand casting process including an external chill 141 and / or an internal chill 142 to pour molten iron having the above-mentioned element content range, the structural density of the ductile iron casting can be further improved through strong quenching. Therefore, by increasing the cooling rate of the molten iron and improving the composition of the molten iron, the comprehensive mechanical properties of various key parts of large-section castings (for example, the main shaft) can be improved.

[0203] Hereinafter, an iron mold casting method of a ductile iron casting according to an embodiment of the present invention will be described.

[0204] The iron mold casting method of the ductile iron casting according to the embodiment of the present invention may include pouring molten iron into a mold cavity 130 formed by a metal outer mold 110 and a sand core 120 .

[0205] The ductile iron castings according to the embodiments of the present invention can be formed by iron mold casting. The schematic diagram of the iron mold according to the embodiment can be the same as the schematic diagram of the sand mold in Figure 3. Therefore, in order to avoid redundancy, the iron mold will be described with reference to Figure 3. The ductile iron castings can be the main shaft of a large-section wind turbine generator set, and can also be the planetary carrier of the gearbox of a large-section wind turbine generator set. In addition, the ductile iron castings are not limited to parts and components in the field of wind power generation, and can also be other ductile iron castings. As an example, the wall thickness of the ductile iron castings can be greater than or equal to 60 mm. For the convenience of description, the iron mold casting method of the ductile iron castings will be described in detail below, taking the ductile iron castings as the main shaft of the wind turbine generator set as an example.

[0206] As shown in FIG3 , the iron mold 100 may include a metal outer mold 110 and a sand core 120 . The internal shape of the metal outer mold 110 may correspond to the external shape of the main shaft 20 . The wall thickness of the metal outer mold 110 may be 100 mm to 200 mm, however, the present invention is not limited thereto. The wall thickness of the metal outer mold 110 may be appropriately adjusted based on the size of the ductile iron casting. Furthermore, the wall thickness of each portion of the metal outer mold 110 may be the same or different, and the present invention does not impose any specific limitations on this.

[0207] The outer shape of the inner sand core 120 is consistent with the inner shape of the main shaft 20. As needed, the metal outer mold 110 and the inner sand core 120 can be divided into multiple sections in the axial direction. For example, the metal outer mold 110 can be divided into at least three sections in the axial direction, and the inner sand core 120 can be divided into at least two sections in the axial direction to facilitate production.

[0208] According to an embodiment of the present invention, the mold cavity 130 may include an axial cavity 131 for forming the shaft body 21, a large flange cavity 132 for forming the large flange 22, a trumpet cavity 133 for forming the trumpet-shaped connector 23, and a small flange cavity 134 for forming the small flange 24. The above division of the mold cavity 130 is a functional division and does not represent a physical division of the structure.

[0209] According to an embodiment of the present invention, the molten iron pouring system (not shown) can be a bottom pouring system or a side pouring system. The specific structural form of the bottom pouring system or the side pouring system is not limited. According to an embodiment of the present invention, the form of the molten iron riser system (not shown) is not specifically limited, for example, it can be a top riser or a side riser.

[0210] According to the embodiments of the present invention, compared to sand casting, the metal outer mold 110 is reusable, thereby reducing costs. Furthermore, the ductile iron castings formed using the metal outer mold 110 have a high surface finish. Furthermore, compared to sand casting, the metal outer mold 110 can effectively increase the cooling rate of the molten iron, refine the grain size, and increase the density of the structure, thereby improving the overall mechanical properties.

[0211] According to the embodiment of the present invention, the inner sand core 120 can effectively absorb the stress during the solidification process of the molten iron, thereby preventing the ductile iron casting from cracking, which is beneficial to improving the comprehensive mechanical properties.

[0212] In addition, the present invention utilizes an iron mold casting process including a metal outer mold 110 and a sand core 120 to pour molten iron with the above-mentioned element content range. By increasing the cooling rate of the molten iron and improving the composition of the molten iron, the comprehensive mechanical properties of various key parts of large-section castings (for example, the main shaft) can be improved.

[0213] The mechanical components of wind turbines in the prior art, especially the main shaft, base and other components of wind turbines, are usually made by forging steel. However, with the development of large-scale wind turbines, the size of the mechanical components in wind turbines has also become larger and larger. Conventional forging methods can no longer meet production requirements. For large-sized mechanical components, casting methods have begun to be used. For example, molten iron is poured into sand molds to form the components. However, sand casting molds use a large amount of sand, and the sand processing system is large and complex, with high energy consumption and high cost. In addition, sand molds cannot be reused and need to be reshaped for each casting, which makes the sand mold manufacturing efficiency low. In addition, due to the low hardness and poor rigidity of the sand mold, it cannot resist the graphitization expansion force generated by the molten iron during the solidification process. Therefore, the castings are prone to shrinkage cavities and shrinkage defects, which affect the quality of the castings and have a low yield rate.

[0214] Therefore, according to one aspect of an embodiment of the present invention, a molding method for manufacturing wind turbine components using an improved mold is provided. Unlike traditional sand molds, the present invention utilizes a metal-coated sand mold. This mold comprises a metal casting mold and a sand coating applied to the inner surface of the metal casting mold, combining the advantages of both metal and sand castings. For example, the metal casting mold can be made of iron.

[0215] According to an embodiment of the present invention, a molding method for a fan component includes the following steps: preparing a molding mold, wherein the molding mold includes an outer mold box and an inner mold core located in the outer mold box, wherein the outer mold box includes a metal casting and a sand coating layer covering the inner cavity surface of the metal casting, and a mold cavity is formed between the mold core and the sand coating layer; and casting molding, wherein molten iron is poured into the mold cavity, and the ductile iron casting is formed after cooling and solidification.

[0216] Below, referring to Figures 8 to 12 , we will describe a method for molding a wind turbine component, a main shaft for a wind turbine generator set, and a wind turbine generator set according to embodiments of the present invention. For convenience, the following description uses the casting of a main shaft for a wind turbine generator set as an example. However, the molding method of the present invention is also applicable to the manufacture of other mechanical components of a wind turbine generator set. Accordingly, the shape and structure of the molding die, particularly the cavity, will vary depending on the specific mechanical component.

[0217] Figure 8 is a perspective view of a main shaft 100 of a wind turbine generator set according to an embodiment of the present invention, and Figure 9 is a cross-sectional view of the main shaft of a wind turbine generator set according to an embodiment of the present invention. The main shaft 100 includes a shaft body 110, a large end flange 120 disposed at one end of the shaft body 110, and a small end flange 130 disposed at the other end of the shaft body 110. The large end flange 120 is used to connect to the hub of the wind turbine generator set, while the small end flange 130 is used to connect to the gearbox of the wind turbine generator set. Due to the significant size difference between the shaft body 110 and the large end flange 120, a flared connecting portion 140 is provided as a transitional connection between the shaft body 110 and the large end flange 120.

[0218] Figure 10 shows a cross-sectional view of a molding die according to an embodiment of the present invention. As shown in Figure 10 , the molding die 200 according to the embodiment of the present invention includes an outer mold box 210 having a hollow interior. The inner surface of the outer mold box 210 has a contour consistent with the outer surface of the spindle 100, and is used to mold the outer contour of the spindle 100.

[0219] To reduce the weight of the spindle 100 and save manufacturing costs, the spindle 100 is typically formed into a hollow structure, as shown in Figure 9 . Therefore, the molding die according to an embodiment of the present invention further includes an inner core 220 , whose outer surface conforms to the contour of the inner cavity surface of the spindle 100 , for molding the inner surface of the spindle 100 . The inner core 220 can be inserted into the outer mold box 210 , with a gap between them, thereby forming a mold cavity 300 that conforms to the shape of the spindle 100 .

[0220] The forming die 200 according to an embodiment of the present invention is a metal mold sand-coated mold. As shown in Figure 10, the outer mold box 210 includes a metal mold 212 and a sand coating 213 covering the inner surface of the metal mold 212. The metal mold 212 can be an iron mold. Compared with traditional sand molds, the forming die according to an embodiment of the present invention has a significant chilling effect during the crystallization process of ductile iron molten iron due to the thin sand coating, which can refine the grain size of the casting and increase the spheroidization rate, and significantly improve the dimensional accuracy and density of the casting. At the same time, due to the presence of the sand coating 213, the graphite expansion of the ductile iron can be utilized to self-compensate the casting to obtain high-quality castings.

[0221] According to an embodiment of the present invention, the weight of the main shaft 100 is approximately 10 tons to 20 tons. In the axial direction of the main shaft 100, the thickness of the main shaft varies, and the wall thickness of the main shaft ranges from 30 mm to 200 mm. Correspondingly, the thickness of the iron casting mold also varies, and the thickness at different positions is different, approximately in the range of 50 mm to 200 mm. In addition, the thickness of the sand coating 113 is 6 mm to 20 mm. The thickness of the sand coating affects the quality of the casting and the production cost. If the thickness of the sand coating is too thick, it not only affects the chilling effect, but also increases the production cost. In addition, an excessively thick sand layer will generate a large amount of gas during the casting process, and the casting is prone to pore defects and is not easy to be uniformly thermally cured. If the thickness of the sand coating is too thin and too heavy, the hardness of the casting will be high, which is not convenient for fine processing.

[0222] According to an embodiment of the present invention, an iron mold with sand coating is used to form a mold, which reduces the amount of sand used and reduces production costs. The iron mold 212 can be reused, and the production efficiency is high. In addition, the obtained casting has high dimensional accuracy, small processing allowance, fine graphite, dense crystal structure, good internal quality of the casting, and high mechanical properties.

[0223] As shown in Figure 10, according to the molding die 200 of the embodiment of the present invention, the outer mold box 210 is divided into three sections, namely the bottom box 214, the middle box 211, and the top box 218. The bottom box 214 corresponds to the end flange of the spindle, and the top box 218 corresponds to the small end flange of the spindle.

[0224] Furthermore, as shown in FIG11 , the middle box can also be divided into multiple sections. For example, the middle box can be divided into three sections, namely a first middle box section 215, a second middle box section 216, and a third middle box section 217. The number of sections of the outer box 210 can be determined based on factors such as the lifting capacity of the lifting mechanism and the height of the sandblasting machine, and is not specifically limited here.

[0225] According to an embodiment of the present invention, the pouring system can be a bottom pouring type, that is, molten iron enters from the bottom of the mold cavity 300. A portion of the pouring pipe can be arranged in the bottom box 214. To facilitate the arrangement of the pouring system in the bottom box 214, the bottom box 214 can be a sand mold box. In addition, the pouring system also includes risers and other components provided in the top box 218. Similarly, to facilitate the formation of risers and other components in the top box 218, the top box 218 can also be a sand mold box. In this case, only the middle box 211 is a sand mold box covered with an iron mold.

[0226] To obtain an iron mold box coated with sand, an iron mold 212 may be prepared first, and then a sandblasting machine may be used to blast sand onto the inner surface of the iron mold to form a sand coating layer.

[0227] As shown in FIG12 , the iron mold 212 is placed on a workbench 310, and an iron mold 330 is placed inside the iron mold 212, thereby forming a sand-shooting cavity 340 between the iron mold 212 and the iron mold 330. The outer ring of the iron mold 330 is aligned with the outer contour of the spindle 100, so that the inner surface of the formed sand coating is aligned with the outer shape of the spindle 100. If the iron mold 212 is segmented, the iron mold 330 also has a corresponding number of segments and a corresponding shape, which will not be described in detail here.

[0228] After the iron mold 212 is arranged, the sandblasting coating operation is performed. Specifically, the iron mold 212 and the iron mold 330 are heated, and sand is injected into the sandblasting cavity 340 using a sandblasting machine 400, allowing the sand to fully solidify between the sand and the iron mold 212. Finally, the mold is removed, resulting in a sand-coated iron mold. By sandblasting each segment of the iron mold and then stacking the multiple segments with the bottom box 214 and top box 218, the outer mold box 210 of the forming mold according to the embodiment of the present invention is obtained.

[0229] According to an embodiment of the present invention, the inner core 220 can adopt a sand core to facilitate demoulding of the casting. The inner core 220 can be directly molded on the bottom box 214. As shown in Figure 10, an exhaust channel 229 can be formed in the middle part of the inner core 220. The exhaust channel extends along the height direction of the inner core 220 and is communicated with the outside of the forming mold so that in the process of molten iron casting, the gas generated by the inner core 220 is discharged in time. A plurality of risers are provided on the top cover 218 for slag removal, exhaust, etc. The exhaust channel 229 in the inner core 220 can be communicated with the riser for exhaust on the top cover 218.

[0230] According to an embodiment of the present invention, when using the mold 200 to manufacture the main shaft 100 of a wind turbine generator set, the outer mold box 210 and / or the inner mold core 220 can be divided into multiple sections along the axial length of the main shaft 100 to facilitate manufacturing. However, the mold 200 according to an embodiment of the present invention is not limited to manufacturing the main shaft of a wind turbine generator set and can also be used to manufacture other mechanical components.

[0231] Furthermore, in order to reduce manufacturing costs, embodiments of the present invention use low-cost ductile iron to manufacture large castings.

[0232] With the continuous development of ductile iron technology, ductile iron has gradually replaced cast steel and become a new type of metal material. As a type of ductile iron, cast ferrite ductile iron has been widely used in engineering machinery, basic parts of injection molding machines, basic parts of die-casting machines, and foundations or key parts of wind power generation. At present, the research on ductile iron for wind power generation mainly focuses on solving how to ensure that the impact energy can still meet the performance requirements at low temperatures while maintaining the existing strength. However, improving the strength while ensuring the low-temperature impact energy is a pair of contradictions. Increasing the strength will inevitably affect the low-temperature impact energy. In order to solve this problem, the present invention provides a ductile iron casting for a wind turbine generator set.

[0233] During the manufacturing and testing of large components for wind turbines, the castings are typically first tested to meet certain performance requirements, such as a tensile strength greater than 400 MPa, a yield strength greater than 280 MPa, and a low-temperature impact energy greater than 7 J at -20°C. Therefore, in the following embodiments of the present invention, the main shaft of a wind turbine is used as an example, with the performance of the casting meeting these requirements as the performance indicator. However, the ductile iron castings of the present invention are not limited to mechanical components of wind turbines; they can also be used for other large-section castings, for example, those with a wall thickness greater than 60 mm.

[0234] The beneficial effects of the present invention will be more clearly described below with reference to the examples and comparative examples of the present invention. The preparation methods in the following examples are conventional methods unless otherwise specified; the reagents and materials used are conventional reagents and materials in the art and can be obtained commercially unless otherwise specified.

[0235] Example 1

[0236] (1) A 20T medium frequency furnace was used, and a high-temperature graphitized recarburizer and Q10 pig iron were charged. The furnace was smelted and recarburized at 1430°C to obtain molten iron. 75% ferrosilicon was added to adjust the silicon content in the molten iron to 1.48wt%; Mn iron was added to adjust the manganese content in the molten iron to 0.125wt%; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0237] The elemental composition of the recarburizer is: carbon greater than 98.5wt%, sulfur less than 0.05wt%, ash less than 0.5wt%, and moisture less than 0.5wt%;

[0238] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0239] Inoculant was laid on one side of the dam in a 20T spheroidizing ladle, and spheroidizing agent and microalloy Ni were laid on the other side of the dam from bottom to top. The microalloy was then covered with cast iron chips with a thickness of 6mm. Molten iron was added to the spheroidizing ladle from the side where the inoculant was laid.

[0240] The amount of inoculant added is 0.54wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.1wt% of the total mass of the molten iron, and the amount of microalloy Ni added is 0.46wt% of the total mass of the molten iron.

[0241] The element composition of the inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0242] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0243] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.14 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0244] The elemental composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0245] The elements of the obtained ductile iron parts include: C 3.71wt%, Si 2.49wt%, Mn 0.125wt%, P 0.025wt%, S 0.02wt%, Ni 0.46wt%, Cr 0.011wt%, Mg 残 0.04wt%, and the rest are iron and inevitable impurities.

[0246] Example 2

[0247] (1) A 20T medium frequency furnace was used, and a high-temperature graphitized recarburizer and Q10 pig iron were charged. The furnace was smelted and recarburized at 1430°C to obtain molten iron. 75% ferrosilicon was added to adjust the silicon content in the molten iron to 1.47wt%; Mn iron was added to adjust the manganese content in the molten iron to 0.122wt%; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0248] The elemental composition of the recarburizer is: carbon greater than 98.5wt%, sulfur less than 0.05wt%, ash less than 0.5wt%, and moisture less than 0.5wt%;

[0249] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0250] The primary inoculant is laid on one side of the dam in the 20T spheroidizing ladle, and the spheroidizing agent, covering inoculant, and microalloy Ni are laid in sequence from bottom to top on the other side of the dam. The microalloy is then covered with cast iron chips with a covering thickness of 6 mm. Molten iron is added into the spheroidizing ladle from the side where the primary inoculant is laid.

[0251] The amount of primary inoculant added is 0.45wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.1wt% of the total mass of the molten iron, the amount of covering inoculant added is 0.09wt% of the total mass of the molten iron; the amount of microalloy Ni added is 0.46wt% of the total mass of the molten iron;

[0252] The element composition of the primary inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0253] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0254] The elemental composition of the cover inoculant is: Si 73.3wt%, C 8.0wt%, Ca 0.45wt%, Ba 1.94wt%, Al 0.52wt%, and the remainder is iron;

[0255] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.14 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0256] The elemental composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0257] The elements of the obtained ductile iron parts include C 3.70wt%, Si 2.47wt%, Mn 0.122wt%, P 0.027wt%, S 0.017wt%, Ni 0.46wt%, Cr 0.009wt%, Mg 残0.05wt%, and the rest are iron and inevitable impurities.

[0258] Example 3

[0259] (1) A 20T medium frequency furnace was used, and a high-temperature graphitized recarburizer and Q10 pig iron were charged. The furnace was smelted and recarburized at 1430°C to obtain molten iron. 75% ferrosilicon was added to adjust the silicon content in the molten iron to 1.45wt%; Mn iron was added to adjust the manganese content in the molten iron to 0.121wt%; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0260] The elemental composition of the recarburizer is: carbon greater than 98.5wt%, sulfur less than 0.05wt%, ash less than 0.5wt%, and moisture less than 0.5wt%;

[0261] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0262] A primary inoculant was laid on one side of the dam in a 20T spheroidizing bag, and a spheroidizing agent, a microalloyed Ni, a microalloyed TiC (the mass ratio of TiC to 75 ferrosilicon was 1:2), and a covering inoculant were laid on the other side of the dam from bottom to top. The microalloyed Ni and the covering inoculant were then covered with cast iron chips to a thickness of 6 mm. Molten iron was added to the spheroidizing bag from the side of the spheroidizing bag where the primary inoculant was laid.

[0263] The amount of primary inoculant added is 0.45wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.1wt% of the total mass of the molten iron, the amount of covering inoculant added is 0.09wt% of the total mass of the molten iron; the amount of microalloy Ni added is 0.45wt% of the total mass of the molten iron; the amount of microalloy TiC added is 0.025wt% of the total mass of the molten iron;

[0264] The element composition of the primary inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0265] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0266] The elemental composition of the cover inoculant is: Si 73.3wt%, C 8.0wt%, V 0.16wt%, Ca 0.45wt%, Ba 1.94wt%, Al 0.52wt%, and the remainder is iron;

[0267] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.14 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0268] The elemental composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0269] The elements of the obtained ductile iron parts include C 3.75wt%, Si 2.45wt%, Mn 0.121wt%, P 0.024wt%, S 0.01wt%, V 0.001wt%, Ni 0.45wt%, Ti 0.021wt%, Cr 0.006wt%, Mg 残 0.04wt%, and the rest are iron and inevitable impurities.

[0270] Example 4

[0271] (1) A 20T medium frequency furnace was used, and a high-temperature graphitized recarburizer and Q10 pig iron were charged. The furnace was smelted and recarburized at 1430°C to obtain molten iron. 75% ferrosilicon was added to adjust the silicon content in the molten iron to 1.15wt%; Mn iron was added to adjust the manganese content in the molten iron to 0.125wt%; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0272] The element composition of the recarburizer is: carbon greater than 98.5%, sulfur less than 0.05%, ash less than 0.5%, and moisture less than 0.5%;

[0273] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0274] Inoculant was laid on one side of the dam in a 20T spheroidizing ladle, and spheroidizing agent and microalloy Ni were laid on the other side of the dam from bottom to top. The microalloy was then covered with cast iron chips with a thickness of 6mm. Molten iron was added to the spheroidizing ladle from the side where the inoculant was laid.

[0275] The amount of inoculant added is 0.75wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.1wt% of the total mass of the molten iron, and the amount of microalloy Ni added is 0.46wt% of the total mass of the molten iron.

[0276] The element composition of the inoculant is: Si 75±3%; Ca 1.0-2.0%; Ba 2.0-3.0%; Al<1.5%, and the rest is iron;

[0277] The elemental composition of the nodularizer is: Si 45.5%, Mg 5.1%, RE 0.243%, Ba 1.31%, Ca 0.94%, and the rest is iron;

[0278] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.14 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0279] The elemental composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0280] The elements of the obtained ductile iron parts include C 3.71wt%, Si 2.31wt%, Mn 0.125wt%, P 0.025wt%, S 0.02wt%, Ni 0.46wt%, Cr 0.011wt%, Mg 残 0.05wt%, and the rest are iron and inevitable impurities.

[0281] Example 5

[0282] (1) A 20T medium frequency furnace was used, and a high-temperature graphitized recarburizer and Q10 pig iron were charged. The furnace was smelted and recarburized at 1430°C to obtain molten iron. 75% ferrosilicon was added to adjust the silicon content in the molten iron to 1.23wt%; Mn iron was added to adjust the manganese content in the molten iron to 0.13wt%; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0283] The element composition of the recarburizer is: carbon greater than 98.5%, sulfur less than 0.05%, ash less than 0.5%, and moisture less than 0.5%;

[0284] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0285] Inoculant was laid on one side of the dam in a 20T spheroidizing ladle, and spheroidizing agent and microalloy Ni were laid on the other side of the dam from bottom to top. The microalloy was then covered with cast iron chips with a thickness of 6mm. Molten iron was added to the spheroidizing ladle from the side where the inoculant was laid.

[0286] Among them, the amount of inoculant added is 0.54wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.1wt% of the total mass of the molten iron; the amount of microalloy Ni added is 0.46wt% of the total mass of the molten iron; the amount of recarburizer added is 0.2wt% of the total mass of the molten iron;

[0287] The element composition of the inoculant is: Si 75±3%; Ca 1.0-2.0%; Ba 2.0-3.0%; Al<1.5%, and the rest is iron;

[0288] The elemental composition of the nodularizer is: Si 45.5%, Mg 5.1%, RE 0.243%, Ba 1.31%, Ca 0.94%, and the rest is iron;

[0289] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.47 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0290] The elemental composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0291] The elements of the obtained ductile iron parts include C 3.71wt%, Si 2.47wt%, Mn 0.13wt%, P 0.024wt%, S 0.017wt%, Ni 0.46wt%, Cr 0.015wt%, Mg 残 0.048wt%, and the rest are iron and inevitable impurities.

[0292] Example 6

[0293] (1) A 20T medium frequency furnace was used, and a high-temperature graphitized recarburizer and Q10 pig iron were charged. The furnace was smelted and recarburized at 1430°C to obtain molten iron. 75% ferrosilicon was added to adjust the silicon content in the molten iron to 1.44wt%; Mn iron was added to adjust the manganese content in the molten iron to 0.125wt%; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0294] The elemental composition of the recarburizer is: carbon greater than 98.5wt%, sulfur less than 0.05wt%, ash less than 0.5wt%, and moisture less than 0.5wt%;

[0295] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0296] Inoculant was laid on one side of the dam in a 20T spheroidizing ladle, and spheroidizing agent and microalloy Ni were laid on the other side of the dam from bottom to top. The microalloy was then covered with cast iron chips with a thickness of 6mm. Molten iron was added to the spheroidizing ladle from the side where the inoculant was laid.

[0297] The amount of inoculant added is 0.75wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.1wt% of the total mass of the molten iron, and the amount of microalloy Ni added is 0.46wt% of the total mass of the molten iron.

[0298] The element composition of the inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0299] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0300] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.14 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0301] The elemental composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0302] The elements of the obtained ductile iron parts include: C 3.71wt%, Si 2.60wt%, Mn 0.125wt%, P 0.025wt%, S 0.02wt%, Ni 0.46wt%, Cr 0.011wt%, Mg 残 0.048wt%, and the rest are iron and inevitable impurities.

[0303] Example 7

[0304] (1) A 20T medium frequency furnace was used, and a high-temperature graphitized recarburizer and Q10 pig iron were charged. The furnace was smelted and recarburized at 1430°C to obtain molten iron. 75% ferrosilicon was added to adjust the silicon content in the molten iron to 1.23wt%; Mn iron was added to adjust the manganese content in the molten iron to 0.14wt%; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0305] The elemental composition of the recarburizer is: carbon greater than 98.5wt%, sulfur less than 0.05wt%, ash less than 0.5wt%, and moisture less than 0.5wt%;

[0306] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0307] Inoculant was laid on one side of the dam in a 20T spheroidizing ladle, and spheroidizing agent and microalloy Ni were laid on the other side of the dam from bottom to top. The microalloy was then covered with cast iron chips with a thickness of 6mm. Molten iron was added to the spheroidizing ladle from the side where the inoculant was laid.

[0308] The amount of inoculant added is 0.54wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.1wt% of the total mass of the molten iron, and the amount of microalloy Ni added is 0.46wt% of the total mass of the molten iron.

[0309] The element composition of the inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0310] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0311] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.47 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0312] The elemental composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0313] The elements of the obtained ductile iron parts include: C 3.71wt%, Si 2.47wt%, Mn 0.14wt%, P 0.025wt%, S 0.02wt%, Ni 0.46wt%, Cr 0.011wt%, Mg 残 0.048wt%, and the rest are iron and inevitable impurities.

[0314] Example 8

[0315] A ductile iron part was prepared in the same manner as in Example 2, except that the addition amount of microalloy Ni in Example 2 was adjusted to 0.2 wt % based on the total mass of the molten iron.

[0316] The elements of the obtained ductile iron parts include C 3.70wt%, Si 2.47wt%, Mn 0.122wt%, P 0.027wt%, S 0.017wt%, Ni 0.20wt%, Cr 0.009wt%, Mg 残0.05wt%, and the rest are iron and inevitable impurities.

[0317] Example 9

[0318] A ductile iron part was prepared in the same manner as in Example 2, except that the addition amount of the microalloy Ni in Example 2 was adjusted to 0.55 wt % of the total mass of the molten iron.

[0319] The elements of the obtained ductile iron parts include C 3.70wt%, Si 2.47wt%, Mn 0.122wt%, P 0.027wt%, S 0.017wt%, Ni 0.55wt%, Cr 0.009wt%, Mg 残 0.05wt%, and the rest are iron and inevitable impurities.

[0320] Comparative Example 1

[0321] (1) A 20T medium frequency furnace was used to charge a high-temperature graphitized recarburizer and Q10 brand pig iron, and smelting and recarburization treatment were performed at 1430°C to obtain molten iron; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0322] The elemental composition of the recarburizer is: carbon greater than 98.5wt%, sulfur less than 0.05wt%, ash less than 0.5wt%, and moisture less than 0.5wt%;

[0323] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0324] Inoculant was laid on one side of the dam in a 20T spheroidizing ladle, and spheroidizing agent and microalloy Ni were laid on the other side of the dam from bottom to top. Then, cast iron chips were used to cover the microalloy with a thickness of 6mm. Molten iron was added into the spheroidizing ladle from the side where the inoculant was laid.

[0325] The amount of inoculant added is 0.5wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.1wt% of the total mass of the molten iron, and the amount of microalloy Ni added is 0.45wt% of the total mass of the molten iron.

[0326] The element composition of the inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0327] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0328] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.15wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0329] The element composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0330] The elements of the obtained ductile iron parts include: C 3.75wt%, Si 2.65wt%, Mn 0.12wt%, P 0.024wt%, S 0.01wt%, Ni 0.45wt%, Mg 残 0.04wt%, and the rest are iron and inevitable impurities.

[0331] Comparative Example 2

[0332] (1) A 20T medium frequency furnace was used to charge a high-temperature graphitized recarburizer and Q10 brand pig iron, and smelting and recarburization treatment were performed at 1430°C to obtain molten iron; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0333] The element composition of the recarburizer is: carbon greater than 98.5%, sulfur less than 0.05%, ash less than 0.5%, and moisture less than 0.5%;

[0334] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0335] Inoculant was laid on one side of the dam in a 20T spheroidizing ladle, and spheroidizing agent and microalloy Ni were laid on the other side of the dam from bottom to top. Then, cast iron chips were used to cover the microalloy with a thickness of 6mm. Molten iron was added into the spheroidizing ladle from the side where the inoculant was laid.

[0336] The amount of inoculant added is 0.54wt% of the total mass of the molten iron, the amount of spheroidizer added is 1.1wt% of the total mass of the molten iron, and the amount of microalloy Ni added is 0.46wt% of the total mass of the molten iron.

[0337] The element composition of the inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0338] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0339] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.14 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0340] The element composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0341] The elements of the obtained ductile iron parts include: C 3.75wt%, Si 2.49wt%, Mn 0.16wt%, P 0.024wt%, S 0.01wt%, Ni 0.46wt%, Mg 残 0.04wt%, and the rest are iron and inevitable impurities.

[0342] Comparative Example 3

[0343] (1) A 20T medium frequency furnace was used to charge a high-temperature graphitized recarburizer and Q10 brand pig iron, and smelting and recarburization treatment were performed at 1430°C to obtain molten iron; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron,

[0344] The element composition of the recarburizer is: carbon greater than 98.5%, sulfur less than 0.05%, ash less than 0.5%, and moisture less than 0.5%;

[0345] (2) spheroidizing, inoculating, and microalloying the molten iron after the carburizing treatment in step (1): laying a primary inoculant on one side of the dam in a 20T spheroidizing bag, and laying a spheroidizing agent, a microalloy Ni, a microalloy TiC (the mass ratio of TiC to 75 ferrosilicon is 1:2), and a covering inoculant on the other side of the dam from bottom to top, and then covering the microalloy and the covering inoculant with cast iron chips to a covering thickness of 6 mm, and adding the molten iron into the spheroidizing bag from the side of the spheroidizing bag where the primary inoculant is laid;

[0346] The amount of primary inoculant added is 0.35wt% of the total mass of the molten iron, the amount of spheroidizing agent added is 1.1wt% of the total mass of the molten iron, the amount of covering inoculant added is 0.09wt% of the total mass of the molten iron; the amount of microalloy Ni added is 0.3wt% of the total mass of the molten iron; the amount of microalloy TiC added is 0.025wt% of the total mass of the molten iron;

[0347] The element composition of the primary inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0348] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0349] The elemental composition of the cover inoculant is: Si 73.3wt%, C 8.0wt%, V 0.16wt%, Ca 0.45wt%, Ba 1.94wt%, Al 0.52wt%, and the remainder is iron;

[0350] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.13 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0351] The elemental composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0352] The elements of the obtained ductile iron parts include C 3.75wt%, Si 2.23wt%, Mn 0.13wt%, P 0.024wt%, S 0.01wt%, V 0.001wt%, Ni 0.46wt%, Ti 0.021wt%, Cr 0.006wt%, Mg 残 0.04wt%, and the rest are iron and inevitable impurities.

[0353] Comparative Example 4

[0354] (1) A 20T medium frequency furnace was used to charge a high-temperature graphitized recarburizer and Q10 brand pig iron, and smelting and recarburization treatment were performed at 1430°C to obtain molten iron; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron,

[0355] The element composition of the recarburizer is: carbon greater than 98.5%, sulfur less than 0.05%, ash less than 0.5%, and moisture less than 0.5%;

[0356] (2) spheroidizing, inoculating, and microalloying the molten iron after the carburizing treatment in step (1): laying a primary inoculant on one side of the dam in a 20T spheroidizing bag, and laying a spheroidizing agent, a microalloy Ni, a microalloy TiC (the mass ratio of TiC to 75 ferrosilicon is 1:2), and a covering inoculant on the other side of the dam from bottom to top, and then covering the microalloy and the covering inoculant with cast iron chips to a covering thickness of 6 mm, and adding the molten iron into the spheroidizing bag from the side of the spheroidizing bag where the primary inoculant is laid;

[0357] The amount of primary inoculant added is 0.41wt% of the total mass of the molten iron, the amount of spheroidizing agent added is 1.1wt% of the total mass of the molten iron, the amount of covering inoculant added is 0.09wt% of the total mass of the molten iron; the amount of microalloy Ni added is 0.6wt% of the total mass of the molten iron; the amount of microalloy TiC added is 0.025wt% of the total mass of the molten iron;

[0358] The element composition of the primary inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0359] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0360] The elemental composition of the cover inoculant is: Si 73.3wt%, C 8.0wt%, V 0.16wt%, Ca 0.45wt%, Ba 1.94wt%, Al 0.52wt%, and the remainder is iron;

[0361] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.13 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0362] The elemental composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0363] The elements of the obtained ductile iron parts include C 3.75wt%, Si 2.33wt%, Mn 0.125wt%, P 0.024wt%, S 0.01wt%, V 0.001wt%, Ni 0.6wt%, Ti 0.021wt%, Cr 0.006wt%, Mg 残 0.04wt%, and the rest are iron and inevitable impurities.

[0364] Comparative Example 5

[0365] (1) A 20T medium frequency furnace was used to charge a high-temperature graphitized recarburizer and Q10 brand pig iron, and smelting and recarburization treatment were performed at 1430°C to obtain molten iron; the amount of recarburizer added was 0.2wt% of the total mass of the molten iron.

[0366] The elemental composition of the recarburizer is: carbon greater than 98.5wt%, sulfur less than 0.05wt%, ash less than 0.5wt%, and moisture less than 0.5wt%;

[0367] (2) spheroidizing, inoculating and microalloying the molten iron after the carburizing treatment in step (1):

[0368] A primary inoculant was laid on one side of the dam in a 20T spheroidizing bag, and a spheroidizing agent, a microalloyed Ni, a microalloyed TiC (the mass ratio of TiC to 75 ferrosilicon was 1:2), and a covering inoculant were laid on the other side of the dam from bottom to top. The microalloyed Ni and the covering inoculant were then covered with cast iron chips to a thickness of 6 mm. Molten iron was added to the spheroidizing bag from the side of the spheroidizing bag where the primary inoculant was laid.

[0369] The amount of the primary inoculant added is 0.45wt% of the total mass of the molten iron, the amount of the spheroidizer added is 1.1wt% of the total mass of the molten iron, and the amount of the microalloy Ni added is 0.15wt% of the total mass of the molten iron.

[0370] The element composition of the inoculant is as follows: Si 75±3wt%; Ca 1.0-2.0wt%; Ba 2.0-3.0wt%; Al<1.5wt%, and the rest is iron;

[0371] The elemental composition of the nodularizer is: Si 45.5wt%, Mg 5.1wt%, RE 0.243wt%, Ba 1.31wt%, Ca 0.94wt%, and the rest is iron;

[0372] (3) Pouring: During the pouring process, a flow-inoculating agent is added for flow-inoculation. The amount of flow-inoculating agent added is 0.14 wt% of the total mass of the molten iron. After the pouring is completed, the casting is slowly cooled in the mold to below 400°C (the slow cooling rate is 10°C / min), and the casting is removed from the mold to obtain a ductile iron casting.

[0373] The element composition of the flow inoculant is: Si 72.09wt%, Bi 1.23wt%, Ca 1.32wt%, Al 1.09wt%, and the rest is iron.

[0374] The elements of the obtained ductile iron parts include: C 3.75wt%, Si 2.45wt%, Mn 0.121wt%, P 0.024wt%, S 0.01wt%, Ni 0.15wt%, Mg 残The molten iron prepared according to the above-described examples and comparative examples was cast into test blocks of ductile iron castings. The ductile iron test blocks were designed according to the GB / T1348-2019 standard and had a thickness of 70 mm to compare the effects of different molten iron compositions on the properties of ductile iron castings.

[0375] 1. Evaluation of the effect of ductile iron

[0376] (1) Tensile strength: tested according to the method specified in GB / T 228.1;

[0377] (2) Yield strength: tested according to the method specified in GB / T 228.1;

[0378] (3) Low-temperature impact toughness at -20℃ shall be tested according to the method specified in GB / T 229.

[0379] The main element composition and specific test results of the ductile iron in the examples and comparative examples are shown in Table 1 below.

[0380] The main element composition of ductile iron was determined by EDS. The instrument used in this experiment was a German Zeiss SUPRA 55 field emission scanning electron microscope combined with an energy dispersive spectrometer.

[0381] Table 1

[0382] According to the experimental data in Table 1 above, it can be seen that the Si, Mn, and Ni contents of the ductile iron test pieces in Examples 1-9 are in the ranges of 2.3-2.6 wt%, ≤0.14 wt%, and 0.20-0.55 wt%, respectively. Therefore, the ductile iron test pieces in Examples 1-9 have a tensile strength greater than 400 MPa, a yield strength greater than 280 MPa, and a low-temperature impact energy greater than 7 J at -20°C.

[0383] The Si content of the ductile iron of Comparative Example 1 exceeds 2.6 wt %, and therefore, the low-temperature impact energy of the ductile iron of Comparative Example 1 at -20°C is less than 7J.

[0384] The Mn content of the ductile iron of Comparative Example 2 exceeds 0.14 wt %. Therefore, the low-temperature impact energy of the ductile iron of Comparative Example 2 at -20°C is less than 7J.

[0385] The Si content of the ductile iron of Comparative Example 3 is less than 2.3 wt %, and therefore, the yield strength of the ductile iron of Comparative Example 3 is less than 280 MPa.

[0386] The Ni content of the ductile iron of Comparative Example 4 is greater than 0.55 wt %. Therefore, the low-temperature impact energy of the ductile iron of Comparative Example 4 at -20°C is less than 7J.

[0387] The Ni content of the ductile iron of Comparative Example 5 is less than 0.20 wt %, and therefore, the tensile strength of the ductile iron of Comparative Example 5 is less than 410 MPa, and the yield strength is less than 280 MPa.

[0388] In the preparation processes of Examples 1 to 3, in step (1), the Si content was controlled to 1.4-1.6 wt%, and the Mn content was controlled to be less than or equal to 0.14 wt%. In step (2), the Ni content was controlled to 0.20-0.55 wt% by microalloying, and a spheroidizing agent and an inoculant were added to control the Si content to 2.25-2.45 wt%. In step (3), a stream-in-stream inoculant was added to control the Si content to 2.3-2.6 wt%.

[0389] In the preparation process of Example 4, the Si content in step (1) was 1.15 wt%, and the Si content was not controlled within the range of 1.4-1.6 wt%. The Si content in step (2) was 2.21 wt%, and the Si content was not controlled within the range of 2.25-2.45 wt%.

[0390] In the preparation process of Example 5, the Si content in step (1) was 1.23 wt%, and the Si content was not controlled within the range of 1.4-1.6 wt%. The Si content in step (2) was 2.13 wt%, and the Si content was not controlled within the range of 2.25-2.45 wt%.

[0391] It can be seen from Table 1 above that, compared with Examples 4 and 5, the ductile iron of Examples 1 to 3 can achieve more excellent technical effects in terms of tensile strength, yield strength and / or low-temperature impact energy at -20°C.

[0392] 2. Metallography of ductile iron

[0393] 2.1 Scanning electron microscopy test

[0394] The scanning electron microscope used in this experiment is a German Zeiss SUPRA 55 field emission scanning electron microscope. Its principle is to use secondary electron signal imaging to observe the sample's surface morphology. The adjustment range is 20V-30kV, with a continuously adjustable adjustment step of 10V, and the magnification range is 12X-1000,000X. The scanning electron microscope is mainly used to observe the tensile fracture morphology, the surface morphology of wear-resistant specimens, and the morphology of thermal fatigue cracks.

[0395] 2.2 Three-dimensional video electron microscopy experiment

[0396] In this test, a Keyence-1000E three-dimensional video electron microscope was used to detect and analyze the tensile and wear specimens. The surface roughness of the specimens was observed based on the photographs taken, and the average scratch depth of the wear surface was calculated.

[0397] 2.3 Test results

[0398] (1) Graphite morphology

[0399] Figure 13A shows the graphite morphology of the ductile iron of Comparative Example 1, and Figure 13B shows the graphite morphology of the ductile iron of Example 1. It can be seen that the graphite in Figure 13B has a higher spheroidization rate and is more evenly distributed than that in Figure 13A .

[0400] (2) Tensile fracture morphology

[0401] Figure 14A shows the tensile fracture morphology of the ductile iron of Comparative Example 1, and Figure 14B shows the tensile fracture morphology of the ductile iron of Example 1. As can be seen from Figure 14B, the fluctuation of the entire cross section is not large at a macroscopic level. The surface morphology of the tensile fracture of the original sample is uneven, and some graphite balls fall off or break during the tensile test, resulting in voids on the cross section surface, indicating that the bonding ability between the graphite balls and the matrix is ​​relatively weak. As can be seen from Figure 14B, compared with the original sample, at a macroscopic level, from the perspective of the overall flatness of the cross section, the roughness and fluctuation of the cross section of the sample increase, and it has a more three-dimensional and layered appearance. At a microscopic level, the separation of the graphite balls from the matrix in the tensile fracture morphology of the sample is greatly reduced, the number of intact graphite balls in the sample increases, and the dispersion is more uniform. Furthermore, in the original specimen in Figure 14A, the fracture morphology features wide and steep "river-like" cleavage steps. The tear ridges produced by ductile fracture are not obvious, and the few remaining ridges have a small number of dimples scattered between them. Compared to the fracture morphology in Figure 14B, the number of tear ridges on the cross section has increased significantly, and the distribution of dimples on the ridges is more uniform and dense. The tear ridges appear bright white, and the ridges are interconnected, forming a network-like closed structure that encloses the graphite nodules.

[0402] (3) Three-dimensional morphology of tensile fracture

[0403] Figure 15A shows the three-dimensional morphology of the tensile fracture of the ductile iron of Comparative Example 1, and Figure 15B shows the three-dimensional morphology of the tensile fracture of the ductile iron of Example 1. Figures 15A and 15B show significant differences in the 3D concavity and convexity of the fracture surfaces of the two specimens. The maximum convex height of the tensile fracture of the specimen in Figure 15A is 596.4 μm, while that of the specimen in Figure 15B is 687.3 μm. This increases the maximum height difference of the tensile fracture by 15.24%. These test results indicate that the toughness of the tensile fracture of the ductile iron of Example 1 has been improved.

[0404] (4) Impact fracture morphology

[0405] FIG16A is the impact fracture morphology of the ductile iron of comparative example 1, and FIG16B is the impact fracture morphology of the ductile iron of example 1. As can be seen from FIG16A, the number of tearing ridges on the fracture of the impact specimen is small, but the size is large. A certain number of coarse dimples are formed around the tearing ridges, and dimple bands are formed in certain parts. At the same time, cleavage planes exist in certain parts of the cross section. This phenomenon can indicate that quasi-cleavage fracture occurs during the fracture process of the impact specimen, which is a mixed fracture. As can be seen from FIG16B, the number of dimples in its fracture has a clear increasing trend compared with the specimen in FIG15A, the length of the tearing ridge has obviously shortened and become thinner, and the curvature has increased. Under the action of impact stress, adjacent dimples can be connected to form a fracture with a certain directionality.

[0406] The ductile iron according to the embodiment of the present invention has a tensile strength greater than 400 MPa, a yield strength greater than 280 MPa, and a low-temperature impact energy greater than 7 J at -20°C, and can be widely used in castings in wind turbines.

[0407] 3. Testing of large-section ductile iron castings cast in sand molds

[0408] In order to test whether the molten iron according to the embodiment of the present invention can also meet the performance requirements of the corresponding casting when cast into a large-section ductile iron casting, the following test is performed.

[0409] The molten iron prepared according to Example 1 and Comparative Example 1 described above was cast into a main shaft through sand casting with chilled iron shown in Figures 4 and 5 and the existing ordinary sand casting without chilled iron (the external chill and the internal chill were removed from Figures 4 and 5), respectively.

[0410] The pouring temperature is 1330-1360°C, and the pouring speed of molten iron is 100-150 kg / s. The dimensions of the main shaft are as follows: the outer diameter of the shaft body 21 is 1500 mm, the outer diameter of the large flange is 2500 mm, and the outer diameter of the small flange is 1500 mm.

[0411] According to the following test methods, samples are taken from the shaft body, large flange, and small flange of the cast main shaft to test the tensile strength, yield strength, and low-temperature impact energy.

[0412] (1) Tensile strength: tested according to the method specified in GB / T 228.1;

[0413] (2) Yield strength: tested according to the method specified in GB / T 228.1;

[0414] (3) Low-temperature impact toughness at -20℃ shall be tested according to the method specified in GB / T 229.

[0415] Table 2

[0416] As shown in Table 2, Example 10 is a spindle made by casting the molten iron of Example 1 into a main shaft by chilled iron sand casting, Comparative Example 6 is a spindle made by casting the molten iron of Example 1 into a main shaft by ordinary sand casting, Comparative Example 7 is a spindle made by casting the molten iron of Comparative Example 1 into a main shaft by chilled iron sand casting, and Comparative Example 8 is a spindle made by casting the molten iron of Comparative Example 1 into a main shaft by ordinary sand casting.

[0417] Compared with comparative example 5, the comprehensive mechanical properties of the shaft body, large flange and small flange of the main shaft of example 6 are significantly improved, indicating that the tensile strength, yield strength and low-temperature impact energy of various parts of the main shaft cast by the cold iron chilled sand casting of the present invention and the molten iron casting of example 1 of the present invention are improved.

[0418] Furthermore, while Comparative Example 7 exhibited higher tensile strength and yield strength, its low-temperature impact energy was significantly reduced, failing to simultaneously improve the tensile strength, yield strength, and low-temperature impact energy of all parts of the main shaft. Furthermore, Comparative Example 8 exhibited no improvement in tensile strength, yield strength, or low-temperature impact energy at all parts of the main shaft. In other words, regardless of whether the molten iron prepared according to Comparative Example 1 was cast using conventional sand casting or chilled sand casting, the overall performance of the main shaft's shaft body, large flange, and small flange was relatively low.

[0419] Therefore, when manufacturing large-section ductile iron castings (for example, large-section fan main shafts) with high performance requirements for each part, the cold iron chilled sand casting method provided by the present invention can be used to cast the molten iron composition provided by the present invention, so that each part of the large-section ductile iron casting (for example, the main shaft) meets the requirements for comprehensive performance.

[0420] According to an embodiment of the present invention, a ductile iron casting formed by the sand casting method can be provided. The ductile iron casting can be a large-section casting, for example, with a wall thickness greater than or equal to 60 mm.

[0421] The ductile iron casting may be the main shaft 20 as described above. According to another embodiment of the present invention, a wind turbine generator system including the main shaft 20 may be provided.

[0422] According to the sand casting method of the ductile iron casting of the present invention, the comprehensive mechanical properties of the ductile iron casting can be improved by controlling the composition of the ductile iron casting and / or the sand casting method.

[0423] According to the sand casting method of the ductile iron casting of the present invention, by controlling the composition of the ductile iron casting, the tensile strength of the ductile iron casting test piece can be made greater than 400 MPa, the yield strength can be made greater than 280 MPa, and the low-temperature impact energy at -20°C can be made greater than 7 J. Therefore, the method can be widely used in the manufacture of ductile iron castings with high comprehensive performance requirements.

[0424] Furthermore, the sand casting method for ductile iron castings according to the present invention can achieve comprehensive performance requirements for various parts of large-section ductile iron castings by utilizing the chilled iron sand casting method according to the present invention to cast the molten iron composition according to the present invention. Therefore, the sand casting method for ductile iron castings according to the present invention can be widely applied to large-section castings for wind turbines and other castings with high comprehensive performance requirements.

[0425] 4. Testing of large-section ductile iron castings cast in iron molds

[0426] In order to test whether the molten iron according to the embodiment of the present invention can also meet the performance requirements of the corresponding casting when cast into a large-section ductile iron casting, the following test is performed.

[0427] The molten iron prepared according to the above-described Example 1 and Comparative Example 1 was cast into a main shaft by iron mold casting and ordinary sand casting, respectively. The wall thickness of the metal outer mold was 200 mm. Ordinary sand casting refers to sand casting without chilling.

[0428] The preheating temperature of the mold cavity for iron casting is 100℃, the pouring temperature is 1330-1360℃, and the pouring speed of molten iron is 100-150kg / s. The pouring temperature of sand casting is 1330-1360℃, and the pouring speed of molten iron is 100-150kg / s.

[0429] The dimensions of the main shaft are as follows: the outer diameter of the shaft body 21 is 1500 mm, the outer diameter of the large flange is 2500 mm, and the outer diameter of the small flange is 1500 mm.

[0430] According to the following test methods, samples are taken from the shaft body, large flange, and small flange of the cast main shaft to test the tensile strength, yield strength, and low impact energy.

[0431] (1) Tensile strength: tested according to the method specified in GB / T 228.1;

[0432] (2) Yield strength: tested according to the method specified in GB / T 228.1;

[0433] (3) Low-temperature impact toughness at -20℃ shall be tested according to the method specified in GB / T 229.

[0434] Table 3

[0435] As shown in Table 3, Example 11 is a main shaft cast by casting the molten iron of Example 1 through iron mold casting, Comparative Example 9 is a main shaft cast by casting the molten iron of Example 1 through ordinary sand casting, Comparative Example 10 is a main shaft cast by casting the molten iron of Comparative Example 1 through iron mold casting, and Comparative Example 11 is a main shaft cast by casting the molten iron of Comparative Example 1 through ordinary sand casting.

[0436] Compared with comparative example 9, the comprehensive mechanical properties of the shaft body, large flange and small flange of the main shaft of example 11 are significantly improved, indicating that the tensile strength, yield strength and low-temperature impact energy of various parts of the main shaft cast by the iron mold casting of the present invention and the molten iron pouring of example 1 of the present invention are improved.

[0437] Furthermore, while Comparative Example 10 exhibited high tensile strength and yield strength, its low-temperature impact energy was significantly reduced, failing to simultaneously improve the tensile strength, yield strength, and low-temperature impact energy of all parts of the main shaft. Furthermore, Comparative Example 11 exhibited no improvement in tensile strength, yield strength, or low-temperature impact energy at all parts of the main shaft. In other words, the overall performance of the main shaft body, large flange, and small flange of the molten iron prepared according to Comparative Example 1 was relatively low, regardless of whether the molten iron was cast using conventional sand casting or iron mold casting.

[0438] Therefore, when manufacturing large-section ductile iron castings (for example, large-section fan main shafts) with high performance requirements for each part, the molten iron composition provided by the present invention can be cast by utilizing the iron mold casting method provided by the present invention, so that each part of the large-section ductile iron casting (for example, the main shaft) meets the requirements for comprehensive performance.

[0439] According to an embodiment of the present invention, a ductile iron casting formed by the above-mentioned iron mold casting method can also be provided. The ductile iron casting can be a large-section casting, for example, with a wall thickness greater than or equal to 60 mm.

[0440] The ductile iron casting may be the main shaft 20 as described above. According to another embodiment of the present invention, a wind turbine generator system including the main shaft 20 may be provided.

[0441] According to the iron mold casting method of the ductile iron casting of the present invention, the comprehensive mechanical properties of the ductile iron casting can be improved by controlling the composition of the ductile iron casting and / or the iron mold casting method.

[0442] According to the iron mold casting method of the ductile iron casting of the present invention, by controlling the composition of the ductile iron casting, the tensile strength of the ductile iron casting test piece can be made greater than 400 MPa, the yield strength can be made greater than 280 MPa, and the low-temperature impact energy at -20°C can be made greater than 7 J. Therefore, the method can be widely used in the manufacture of ductile iron castings with high comprehensive performance requirements.

[0443] Furthermore, the iron mold casting method for ductile iron castings according to the present invention can achieve comprehensive performance requirements for various parts of the ductile iron castings by pouring the molten iron composition according to the present invention. Therefore, the iron mold casting method for ductile iron castings according to the present invention can be widely applied to large-section castings for wind turbines and other castings with high comprehensive performance requirements.

[0444] 5. Performance test of large ductile iron castings cast in iron mold covered with sand

[0445] According to an embodiment of the present invention, by adopting a metal mold coated with sand, the strong chilling of the metal mold can be used to further improve the microstructure density of ductile iron castings. Therefore, by increasing the cooling rate of the molten iron and improving the composition of the molten iron, the comprehensive mechanical properties of large castings can be improved. Below, the molten iron prepared according to the above-described embodiment 1 is used as an example to cast the main shaft of a wind turbine generator set through the iron mold coated with sand mold according to the embodiment of the present invention and the ordinary sand mold to test whether the molten iron according to the embodiment of the present invention can also meet the performance requirements of the casting when casting large castings. The outer diameter of the main shaft shaft 110 is 1500mm. The pouring temperature is 1330-1360℃, and the pouring speed of the molten iron is 100-150kg / s.

[0446] Example 12

[0447] The same materials as in Example 1 were used, and an iron-coated sand mold according to an embodiment of the present invention was used to cast the main shaft of the wind turbine generator set. That is, Example 12 used exactly the same materials and process control procedures as Example 1. The difference was that Example 1 used a traditional sand mold to cast the ductile iron specimen, while Example 12 used an iron-coated sand mold according to an embodiment of the present invention to cast the main shaft of the wind turbine generator set.

[0448] Comparative Example 12

[0449] Compared with Example 12, Comparative Example 12 uses the same materials and process control procedures as Example 12. The difference is that Example 12 uses the iron mold covered with sand mold according to the embodiment of the present invention to manufacture the main shaft of the wind turbine, while Comparative Example 12 uses traditional sand molds to cast the main shaft of the wind turbine.

[0450] Comparative Example 13

[0451] Compared with Example 12, Comparative Example 13 uses the same materials and process control procedures. The difference is that Example 12 uses the iron mold covered with sand according to the embodiment of the present invention to manufacture the main shaft of the wind turbine, while Comparative Example 13 uses a traditional iron mold to cast the main shaft of the wind turbine.

[0452] Samples were taken from the shaft body, large end flange, and small end flange of the cast main shaft according to the following test methods to test the tensile strength, yield strength, and low-temperature impact energy:

[0453] (1) Tensile strength: tested according to the method specified in GB / T 228.1;

[0454] (2) Yield strength: tested according to the method specified in GB / T 228.1;

[0455] (3) Low-temperature impact toughness at -20℃ shall be tested according to the method specified in GB / T 229.

[0456] The specific test results of the spindles in Example 12 and Comparative Example 12 are shown in Table 2 below.

[0457] Table 4

[0458] As shown in Table 4, when the molten iron obtained according to Example 1 of the present invention is cast using an iron mold coated with sand, the low-temperature impact energy of the main shaft can be significantly improved, meeting the comprehensive performance requirements of the main shaft. However, when the molten iron prepared according to Example 1 of the invention is cast into a main shaft using a traditional sand casting process, the shaft body, large end flange and small end flange of the main shaft cannot simultaneously meet the comprehensive performance requirements of the main shaft. When the main shaft is prepared using an iron mold, the overall comprehensive performance requirements of the main shaft can be met, but the effect of improving the low-temperature impact energy is not as good as the low-temperature impact energy of the main shaft obtained by the iron mold coated with sand forming mold. Therefore, when manufacturing large-scale fan components with high performance requirements for each part, the molten iron composition provided by the embodiment of the present invention and the iron mold coated with sand process provided by the embodiment of the present invention can be used for casting, thereby significantly improving the low-temperature impact energy, so that each part of the large ductile iron casting meets the requirements for comprehensive performance.

[0459] In addition, compared with the existing sand molding process, the use of the iron mold sand coating process to manufacture ductile iron castings according to the embodiments of the invention also has the following technical effects: 1) High dimensional accuracy. The dimensional accuracy of the castings obtained by the iron mold sand coating process can reach CT10, while the accuracy of the castings obtained by the sand molding process is CT12; 2) More compact structure and high UT grade. The UT grade of the main shaft obtained by the iron mold sand coating process can reach UT1, while the UT grade of the main shaft obtained by the sand molding process is UT2-3; 3) Faster cooling time, saving 3 days of unpacking time compared with the sand molding process; 4) Improved utilization of the sand box and site, thereby increasing the production capacity per unit area.

[0460] Comparative Example 14

[0461] In Comparative Example 14, the molten iron obtained in Comparative Example 1 was used to manufacture the main shaft of the wind turbine generator set through a sand molding process.

[0462] Comparative Example 15

[0463] In Comparative Example 15, the molten iron obtained in Comparative Example 1 was used to manufacture the main shaft of a wind turbine generator set using an iron mold.

[0464] Comparative Example 16

[0465] In Comparative Example 16, the molten iron obtained in Comparative Example 1 was used to manufacture the main shaft of a wind turbine generator set using the iron mold coated with sand mold provided by an embodiment of the present invention.

[0466] In the above comparative examples 14, 15 and 16, the main shaft of the wind turbine generator set was manufactured by using the molten iron obtained in comparative example 1, respectively using a traditional sand mold, a traditional iron mold and an iron mold coated with sand mold according to an embodiment of the present invention. After sampling various parts of the main shaft, performance tests were carried out. The performance test data are compared in Table 5 below.

[0467] Table 5

[0468] It can be seen from Table 5 that for molten iron with ordinary material composition, no matter it is an ordinary sand mold, an ordinary iron mold or an iron mold covered with sand mold, the main shaft obtained is difficult to meet the comprehensive performance requirements.

[0469] In summary, the ductile iron casting test block according to the embodiment of the present invention has excellent comprehensive performance, especially for the casting test block with a large cross-section, it can obtain excellent performance of a tensile strength greater than 400 MPa, a yield strength greater than 280 MPa, and a low-temperature impact energy greater than 7 J at -20°C. Therefore, it can be widely used in the manufacture of ductile iron castings with high comprehensive performance requirements.

[0470] In addition, the ductile iron castings obtained using the molten iron obtained according to the embodiment of the present invention and the iron mold sand coating process according to the embodiment of the present invention have excellent comprehensive performance. In particular, the low-temperature impact energy of the main shaft of the wind turbine generator set can be greatly improved, reducing the risk of fracture in low-temperature environments. Therefore, the iron mold sand coating mold of the ductile iron casting according to the present invention can be widely used for large castings in wind turbines, and can also be used for castings in other fields with higher comprehensive performance requirements, especially large-section castings, and can also meet the comprehensive performance requirements.

[0471] While exemplary embodiments of the present invention have been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims.

Claims

1. A ductile iron, characterized in that, Based on the total mass of the ductile cast iron, the ductile cast iron comprises, by mass percentage: C 3.6 - 3.8 wt%, Si 2.3 - 2.6 wt%, Mn ≤ 0.14 wt%, Ni 0.20 - 0.55 wt%.

2. The ductile cast iron according to claim 1, characterized in that, The ductile cast iron further comprises, by mass percentage: V 0.001 - 0.01 wt%, Ti 0.02 - 0.03 wt%.

3. The ductile cast iron according to claim 1, wherein, The ductile iron further includes, by mass percentage: P ≤ 0.035 wt%, S ≤ 0.02 wt%, Cr ≤ 0.025 wt%, Mg 残 0.035 - 0.060 wt%.

4. The ductile cast iron according to claim 1, characterized in that, The matrix of the ductile cast iron is ferrite.

5. The ductile cast iron according to claim 1, characterized in that, The content of Si is in the range of 2.30 - 2.49 wt%.

6. The ductile cast iron according to claim 1, characterized in that, The content of Si is in the range of 2.35 - 2.49 wt%.

7. The ductile cast iron according to claim 6, characterized in that, The content of Si is in the range of 2.39 - 2.45 wt%.

8. The ductile cast iron according to claim 1, characterized in that, The content of Si is in the range of 2.30 - 2.40 wt%.

9. The ductile cast iron according to claim 1, wherein The content of Mn is in the range of 0.10 - 0.12 wt%.

10. The ductile cast iron according to claim 3, characterized in that, The content of S is less than 0.015 wt%.

11. The ductile cast iron according to claim 1, characterized in that, The content of Ni is in the range of 0.35 - 0.55 wt%.

12. The ductile cast iron according to claim 11, characterized in that, The content of Ni is in the range of 0.35 - 0.45 wt%.

13. The ductile cast iron according to claim 3, characterized in that, Mg 残 The content of is in the range of 0.040 - 0.054 wt%.

14. The ductile cast iron according to any one of claims 1 to 13, characterized in that, The tensile strength of the ductile cast iron is greater than 400 Mpa, the yield strength is greater than 280 Mpa, and the low-temperature impact energy at -20 °C is greater than 7 J.

15. A ductile iron casting, characterized in that, The ductile cast iron part comprises the ductile cast iron according to any one of claims 1 to 13.

16. The ductile iron casting according to claim 15, characterized in that, The wall thickness of the ductile cast iron part is greater than or equal to 60 mm.

17. A method for preparing ductile iron, characterized in that, The preparation method comprises the following steps: (1) Melting: Carrying out carbon addition treatment on the materials including pig iron and melting them into molten iron; (2) Spheroidizing and inoculating: Spheroidizing and inoculating the molten iron obtained from step (1); and (3) Pouring: Pouring the molten iron obtained from step (2), wherein, in step (1) and / or step (2), the preparation method further comprises microalloying treatment, and the microalloying treatment includes adding Ni, adding a spheroidizing agent containing Si and an inoculant containing Si in step (2) and adding a stream inoculant containing Si in step (3), wherein, based on the total mass of the molten iron, the content of Ni is 0.20 - 0.55 wt%, the content of Si is 2.3 - 2.6 wt%, and the content of Mn is less than or equal to 0.14 wt%.

18. The preparation method according to claim 17, characterized in that, Based on the total mass of the molten iron, in step (1), the content of Si included in the materials is in the range of 1.4 - 1.6 wt%, in step (2), adding a spheroidizing agent containing Si and an inoculant containing Si such that the content of Si is in the range of 2.25 - 2.45 wt%, and in step (3), adding a stream inoculant containing Si such that the content of Si is in the range of 2.3 - 2.6 wt%.

19. The preparation method according to claim 17, wherein based on the total mass of the spheroidizing agent, the spheroidizing agent comprises 40 - 50 wt% of Si by mass percentage, based on the total mass of the inoculant, the inoculant comprises 72 - 78 wt% of Si by mass percentage, based on the total mass of the stream inoculant, the stream inoculant comprises 70 - 80 wt% of Si by mass percentage.

20. The preparation method according to claim 19, wherein Based on the total mass of the inoculant, the inoculant comprises, by mass percentage: 72 - 78 wt% of Si, 1.0 - 2.0 wt% of Ca, 2.0 - 3.0 wt% of Ba, < 1.5 wt% of Al, and the balance being iron. Based on the total mass of the spheroidizing agent, the spheroidizing agent comprises, by mass percentage: 4.5 - 6 wt% of Mg, 0.15 - 0.3 wt% of RE, 40 - 50 wt% of Si, and the balance being iron. Based on the total mass of the in - stream inoculant, the in - stream inoculant comprises, by mass percentage: 70 - 80 wt% of Si, 0.5 - 2.5 wt% of Bi, ≤ 2.0 wt% of Ca, ≤ 2.0 wt% of Al, and the balance being Fe.

21. The preparation method according to claim 19, wherein in step (2), the addition amount of the inoculant is 0.35 - 0.67 wt% of the total mass of the molten iron, the addition amount of the spheroidizing agent is 1.0 - 1.3 wt% of the total mass of the molten iron, in step (3), the addition amount of the in - stream inoculant is 0.08 - 0.2 wt% of the total mass of the molten iron.

22. The preparation method according to claim 21, characterized in that, The inoculant in step (2) includes a primary inoculant and a covering inoculant, wherein, based on the total mass of the primary inoculant, the primary inoculant comprises, by mass percentage, 72 - 78 wt% of Si, wherein, based on the total mass of the covering inoculant, the covering inoculant comprises, by mass percentage, 72 - 78 wt% of Si.

23. The preparation method according to claim 22, wherein based on the total mass of the primary inoculant, the primary inoculant comprises, by mass percentage: 72 - 78 wt% of Si, 1.0 - 2.0 wt% of Ca, 2.0 - 3.0 wt% of Ba, < 1.5 wt% of Al, and the balance being iron, based on the total mass of the covering inoculant, the covering inoculant comprises, by mass percentage: 72 - 78 wt% of Si, 1.0 - 2.0 wt% of Ca, 2.0 - 3.0 wt% of Ba, < 1.5 wt% of Al, and the balance being iron.

24. The preparation method according to claim 22, characterized in that, In step (2), the addition amount of the primary inoculant is 0.30 - 0.55 wt% of the total mass of the molten iron, the addition amount of the covering inoculant is 0.05 - 0.12 wt% of the total mass of the molten iron.

25. The preparation method according to claim 17, wherein Mg is added in step (2) such that, based on the total mass of the molten iron, the content of Mg is in the range of 0.045 - 0.078 wt%.

26. The preparation method according to claim 25, wherein based on the total mass of the spheroidizing agent, the spheroidizing agent comprises 4.5 - 6.5 wt% of Mg, and the addition amount of the spheroidizing agent in step (2) is 1.0 - 1.3 wt% of the total mass of the molten iron.

27. The preparation method according to claim 17, wherein, In step (1) and / or step (2), the addition amount of Ni is 0.2 - 0.4 wt% of the total mass of the molten iron.

28. The preparation method according to claim 17, wherein The micro - alloy treatment in step (1) and / or step (2) includes adding Ni such that the content of Ni is in the range of 0.20 - 0.55 wt% of the total mass of the molten iron.

29. The preparation method according to claim 17, wherein In step (1) and / or step (2), the microalloy treatment further includes adding TiC to the molten iron, wherein the addition amount of TiC is 0.01-0.03 wt% of the total mass of the molten iron.

30. The preparation method according to claim 17, characterized in that, The pig iron in step (1) is pig iron of grade Q10 or above.

31. The preparation method according to claim 17, characterized in that, Based on the total mass of the molten iron, the content of Mn is in the range of 0.10-0.12 wt%.

32. The preparation method according to claim 17, characterized in that, Adjust the content of Mn in step (1) so that the content of Mn in step (1) is in the range of 0.10-0.12 wt% of the total mass of the molten iron.

33. The preparation method according to claim 17, characterized in that, Based on the total mass of the molten iron, the content of Ni is 0.35-0.45 wt%.

34. The preparation method according to claim 17, characterized in that, Based on the total mass of the molten iron, the content of V is 0.001-0.01 wt%.

35. The preparation method according to claim 17, characterized in that, Based on the total mass of the molten iron, the content of Si is 2.39-2.45 wt%.

36. The preparation method according to claim 17, wherein Based on the total mass of the molten iron, the content of Si is 2.30-2.40 wt%.

37. A ductile cast iron produced by the production method according to any one of claims 17 to 30, characterized in that, Based on the total mass of the ductile iron, the ductile iron comprises by mass percentage: C 3.6-3.8 wt%, Si 2.3-2.6 wt%, Mn≤0.14 wt%, Ni 0.20-0.55 wt%.

38. The ductile cast iron according to claim 37, characterized in that, The ductile iron includes, by mass percentage: Si 2.39 - 2.45 wt%, Mn 0.10 - 0.12 wt%, Ni 0.35 - 0.45 wt%, P ≤ 0.035 wt%, S ≤ 0.02 wt%, Cr ≤ 0.025 wt%, Mg 残 0.040 - 0.054 wt%.

39. A ductile cast iron produced by the production method according to any one of claims 17 to 30, characterized in that, Based on the total mass of the ductile iron, the ductile iron comprises by mass percentage: C 3.6-3.8 wt%, Si 2.3-2.6 wt%, Mn≤0.14 wt%, V 0.001-0.01 wt%, Ni 0.20-0.55 wt%, Ti 0.02-0.03 wt%.

40. A ductile iron casting prepared by the preparation method according to any one of claims 17 to 36.

41. The ductile iron casting according to claim 40, characterized in that, The wall thickness of the ductile iron casting is greater than or equal to 60 mm.

42. A method for casting ductile iron castings in an iron mold, characterized in that, The iron mold casting method includes pouring the molten iron into a cavity (130) formed by a metal outer mold (110) and a sand core (120), and the ductile iron casting comprises by mass percentage: C 3.6-3.8 wt%, Si 2.3-2.6 wt%, Mn≤0.14 wt%, Ni 0.20-0.55 wt%.

43. The iron mold casting method according to claim 42, characterized in that, The molten iron is prepared by the preparation method according to any one of claims 17 to 36.

44. The iron mold casting method of the ductile iron casting according to claim 42, characterized in that, Before pouring the molten iron into the cavity (130), preheat the temperature of the cavity (130) to 50-200 °C, The pouring temperature of the molten iron is 1330-1360 °C, and the pouring speed of the molten iron is 100-150 kg / s.

45. A ductile iron casting, characterized in that, The ductile iron casting is formed by the iron mold casting method according to any one of claims 42 and 43.

46. The ductile iron casting according to claim 45, wherein The wall thickness of the ductile iron casting is greater than or equal to 60 mm.

47. The ductile iron casting according to claim 45, characterized in that, The ductile iron casting is the main shaft (20) of a wind turbine generator, and the main shaft (20) includes a shaft body (21), a large flange (22) arranged at one axial end of the shaft body (21), a trumpet-shaped connecting member (23) connecting the shaft body (21) and the large flange (22), and a small flange (24) arranged at the other axial end of the shaft body (21), The outer diameter of the shaft body (21) is greater than or equal to 1.0 m.

48. A sand casting device for a fan main shaft, the sand casting device comprising a sand mold (100), the sand mold (100) including an outer sand mold (110) and an inner sand core (120) and a cavity (130) surrounded by the outer sand mold (110) and the inner sand core (120). It is characterized in that The sand mold (100) further includes an external chill (141) and / or an internal chill (142), the external chill (140) being disposed around the cavity (130) in the outer sand mold (110) and exposed from the cavity (130), and the internal chill (142) being disposed around the cavity (130) in the inner sand core (120) and exposed from the cavity (130).

49. The sand casting device for the fan main shaft according to claim 48, characterized in that, The ratio of the thickness of the external chill (141) and / or the internal chill (142) to the thickness of the portion of the fan main shaft (20) covered by the external chill (141) and / or the internal chill (142) is 0.5 - 1.

5.

50. The sand casting device for the main shaft of a fan according to claim 48 or 49, characterized in that, The fan main shaft (20) includes a shaft body (21), a large flange (22) provided at one axial end of the shaft body (21), a bell-shaped connecting member (23) connecting the shaft body (21) and the large flange (22), and a small flange (24) provided at the other axial end of the shaft body (21).

51. The sand casting device for the fan main shaft according to claim 50, characterized in that, The external chill (141) includes a first formed chill (141a) and a second formed chill (141b), the first formed chill (141a) being disposed at a position corresponding to the upper end face of the large flange (22) and the outer peripheral face of the bell-shaped connecting member (23), and the second formed chill (141b) being disposed at a position corresponding to the lower end face of the large flange (22).

52. The sand casting device for a fan main shaft according to claim 51, characterized in that, Each of the first formed chill (141a) and the second formed chill (141b) forms at least two segments around the cavity (130).

53. The sand casting device for the fan main shaft according to claim 51, characterized in that, The thickness of each of the first formed chill (141a) and the second formed chill (141b) is greater than or equal to 200 mm.

54. The sand casting device for a fan main shaft according to claim 51, characterized in that, The coverage rate of the first formed chill (141a) is greater than or equal to 90%, and / or the coverage rate of the second formed chill (141b) is greater than or equal to 80%.

55. The sand casting device for a fan main shaft according to claim 50, characterized in that, The external chill (141) is further disposed at positions corresponding to the outer peripheral face of the shaft body (21) and the outer peripheral face and / or upper end face of the small flange (24).

56. The sand casting device for a fan main shaft according to claim 50, characterized in that, The internal chill (142) is disposed at a position corresponding to the inner peripheral face of the bell-shaped connecting member (23).

57. The sand casting device for the fan main shaft according to claim 56, characterized in that, The internal chill (142) is further disposed at a position corresponding to the inner end face of the small flange (24).

58. The sand casting device for a fan main shaft according to claim 48, characterized in that, The sand casting device further includes a gating system, and the gating system is a bottom gating system.

59. The sand casting device for the fan main shaft according to claim 51, characterized in that, The sand mold (100) includes risers, and the risers include at least one of a top riser (151), an intermediate-section riser (152), and a hot riser (153). The top riser (151) is disposed at a position corresponding to the outer end of the small flange (24), the intermediate-section riser (152) is disposed at a position corresponding to the outer wall of the shaft body (21), and the hot riser (153) is disposed at a position corresponding to the inner cavity of the bell-shaped connector (23).

60. A fan main shaft, characterized in that, The main shaft of the fan is formed by using the sand casting device according to any one of claims 48 to 59.

61. The main shaft of the fan according to claim 60, characterized in that, The outer diameter of the shaft body (21) of the main shaft (20) of the fan is greater than or equal to 1.0 m.

62. A sand casting method for a ductile iron casting, the sand casting method comprising: Preparing a mold; Preparing a sand mold (100), and using the mold to prepare the sand mold (100), the sand mold (100) including a cavity (130); Pouring and molding, pouring molten iron into the cavity (130), and forming the ductile iron casting after cooling and solidifying, wherein the ductile iron casting includes, by mass percentage: C 3.6 - 3.8 wt%, Si 2.3 - 2.6 wt%, Mn ≤ 0.14 wt%, Ni 0.20 - 0.55 wt%.

63. The sand casting method of ductile iron castings according to claim 62, characterized in that, The sand mold (100) is the sand mold (100) according to any one of claims 48 to 59.

64. The sand casting method for a ductile iron casting according to claim 62, wherein the pouring temperature of the molten iron is 1330 - 1360 °C, and the pouring speed of the molten iron is 100 - 150 kg / s.

65. A ductile iron casting, characterized in that, The ductile iron casting is formed by using the sand casting method according to any one of claims 62 to 64.

66. The ductile iron casting according to claim 65, wherein, The wall thickness of the ductile iron casting is greater than or equal to 60 mm.

67. The ductile iron casting according to claim 65, characterized in that, The ductile iron casting is the main shaft (20) of a wind turbine generator, and the main shaft (20) includes a shaft body (21), a large flange (22) disposed at one axial end of the shaft body (21), a bell-shaped connector (23) connecting the shaft body (21) and the large flange (22), and a small flange (24) disposed at the other axial end of the shaft body (21). The outer diameter of the shaft body (21) is greater than or equal to 1.0 m.

68. A casting forming die for forming cast iron parts, characterized in that, The casting mold includes an outer mold box and an inner core disposed in the outer mold box. The outer mold box includes a metal casting mold and a sand coating layer covering the inner surface of the cavity of the metal casting mold. A casting cavity is formed between the outer mold box and the inner core, and molten iron can be poured into the casting cavity and cooled and formed into a cast iron casting in the cavity.

69. The casting forming mold according to claim 68, wherein, The metal casting mold is an iron mold, the thickness of the iron mold is 50 mm - 200 mm, and the thickness of the sand coating layer is 6 mm - 20 mm.

70. The molding die according to claim 68, wherein, The outer mold box includes a bottom box, a top box, and a middle box disposed between the bottom box and the top box. The middle box is an iron mold sand-coated box, the top box and the bottom box are sand boxes, and the inner core is a sand core.

71. The casting forming die according to claim 70, characterized in that, The middle box is divided into multiple sections.

72. The casting forming mold according to claim 70, characterized in that, The casting forming die further includes a bottom gating system, and a runner for conveying molten iron into the cavity is arranged in the bottom box.

73. The casting forming die according to claim 70, wherein, A riser is arranged in the top box, and an exhaust passage is arranged in the inner core, and the exhaust passage communicates with the riser.

74. The casting mold according to claim 70, wherein, In the height direction of the die, the outer mold box and / or the inner core are divided into multiple sections.

75. The casting forming die according to claim 70, wherein, The casting is the main shaft of a wind turbine generator, the main shaft includes a shaft body, a large-end flange connected to one end of the shaft body, and a small-end flange connected to the other end of the shaft body. There is also a flared connecting section between the large-end flange and the shaft body. The bottom box corresponds to the large-end flange, the middle box corresponds to the shaft body and the flared connecting section, and the top box corresponds to the small-end flange.

76. A ductile iron casting, characterized in that, The ductile iron casting is made by using the casting forming die according to any one of claims 68-75.

77. The ductile iron casting according to claim 76, characterized in that, The ductile iron casting is the main shaft of a wind turbine generator, and the outer diameter of the shaft body of the main shaft is greater than or equal to 1 m.

78. A forming method for ductile iron castings, characterized in that, The forming method includes: Preparing a forming die, the forming die includes an outer mold box and an inner core located in the outer mold box. The outer mold box includes a metal casting mold and a sand coating layer covering the inner cavity surface of the metal casting mold. A cavity is formed between the outer mold box and the inner core. Performing casting forming, pouring molten iron into the cavity, and forming the ductile iron casting after cooling and solidification. Wherein, the ductile iron casting includes, by mass percentage: C 3.6-3.8 wt%, Si 2.3-2.6 wt%, Mn ≤ 0.14 wt%, Ni 0.20-0.55 wt%.

79. The forming method according to claim 78, characterized in that, The molten iron is prepared by the preparation method according to any one of claims 17 to 36.

80. A wind turbine generator, characterized in that, The wind turbine generator includes the ductile iron casting according to any one of claims 15, 40, 45 to 47, 65 to 67, 76 and 77.

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